Oligohydramnios (Clinical)

Overview

Definition

Decreased amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity volume for gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care is referred to as oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios. Oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios is diagnosed based on ultrasound measurements of amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity volume and can be defined as either:

• Amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity index (AFI) ≤ 5 cm 
• Single deep pocket (SDP) of < 2 cm

Anhydramnios Anhydramnios An extreme case of oligohydramnios with no measurable pockets of amniotic fluid present. Oligohydramnios is an extreme case of oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios with no measurable pockets of amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity present.

Epidemiology^[4,5,8,9]

• Incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency rates are highly variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables and based on gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care and associated risk factors.
• Incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency rates based on gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care:
  • Overall incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency in term pregnancies of 37–42 weeks: 4.4%
  • More common in pregnancies > 40 weeks: 11%
  • Less common in preterm pregnancies of < 37 weeks: < 1% 
• Most cases of oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios are diagnosed in the 3rd trimester of pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care with no identifiable cause.

Pathophysiology and Etiology

Normal amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity production^[5,7,9]

Amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity volume is determined by the volume of fluid flowing into and out of the amniotic sac. The main contributors are:

• Fetal urination (primary source of fluid 2nd half of pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care)
• Fetal swallowing Swallowing The act of taking solids and liquids into the gastrointestinal tract through the mouth and throat. Gastrointestinal Motility (removal of amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity)
• Lung secretions
• Transport of maternal plasma Plasma The residual portion of blood that is left after removal of blood cells by centrifugation without prior blood coagulation. Transfusion Products across the fetal membranes as a result of hydrostatic and oncotic forces

Pathogenesis^[5,7]

Oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios is a result of decreased fluid production in relation to fluid removal.

• Primarily due to ↓ fetal urine production in the 2nd half of pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care
• Note: Other physiologic alterations do not play significant roles in the development of oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios for the following reasons:
  • In general, ↑ swallowing Swallowing The act of taking solids and liquids into the gastrointestinal tract through the mouth and throat. Gastrointestinal Motility does not occur.
  • Lung secretions do not contribute enough to the amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity volume in the 2nd half of pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care to have an impact.
  • Transfer of fluid across the amnion Amnion The innermost membranous sac that surrounds and protects the developing embryo which is bathed in the amniotic fluid. Amnion cells are secretory epithelial cells and contribute to the amniotic fluid. Placenta, Umbilical Cord, and Amniotic Cavity is more successful in preventing polyhydramnios Polyhydramnios Polyhydramnios is a pathological excess of amniotic fluid. Common causes of polyhydramnios include fetal anomalies, gestational diabetes, multiple gestations, and congenital infections. Patients are often asymptomatic but may present with dyspnea, extremity swelling, or abdominal distention. Polyhydramnios (excess amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity) than oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios (fluid outflow is easier than inflow).
• ↓ Amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity volume → compression Compression Blunt Chest Trauma:
  • Abdominal compression Compression Blunt Chest Trauma (especially in the 2nd trimester) → limits movement of the diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm: Anatomy → pulmonary hypoplasia Hypoplasia Hypoplastic Left Heart Syndrome (HLHS) (poor outcome)
  • Musculoskeletal deformities (e.g., club foot Foot The foot is the terminal portion of the lower limb, whose primary function is to bear weight and facilitate locomotion. The foot comprises 26 bones, including the tarsal bones, metatarsal bones, and phalanges. The bones of the foot form longitudinal and transverse arches and are supported by various muscles, ligaments, and tendons. Foot: Anatomy, arthrogryposis)
  • Umbilical cord Umbilical cord The flexible rope-like structure that connects a developing fetus to the placenta in mammals. The cord contains blood vessels which carry oxygen and nutrients from the mother to the fetus and waste products away from the fetus. Placenta, Umbilical Cord, and Amniotic Cavity compression Compression Blunt Chest Trauma → ↓ tolerance Tolerance Pharmacokinetics and Pharmacodynamics for uterine contractions in labor

Etiology^[5,7,9]

Specific etiologies leading to oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios include:

• Idiopathic Idiopathic Dermatomyositis (possibly due to alterations in aquaporin channels Channels The Cell: Cell Membrane in the fetal membranes and placenta Placenta A highly vascularized mammalian fetal-maternal organ and major site of transport of oxygen, nutrients, and fetal waste products. It includes a fetal portion (chorionic villi) derived from trophoblasts and a maternal portion (decidua) derived from the uterine endometrium. The placenta produces an array of steroid, protein and peptide hormones (placental hormones). Placenta, Umbilical Cord, and Amniotic Cavity)
• Prelabor rupture of membranes Prelabor Rupture of Membranes Prelabor rupture of membranes (PROM), previously known as premature rupture of membranes, refers to the rupture of the amniotic sac before the onset of labor. Prelabor rupture of membranes may occur in term or preterm pregnancies. Prelabor Rupture of Membranes ( PROM PROM Prelabor rupture of membranes (PROM), previously known as premature rupture of membranes, refers to the rupture of the amniotic sac before the onset of labor. Prelabor rupture of membranes may occur in term or preterm pregnancies. Prelabor Rupture of Membranes) with a “small/slow leak” 
• Placental insufficiency Placental Insufficiency Failure of the placenta to deliver an adequate supply of nutrients and oxygen to the fetus. Neonatal Polycythemia: poor oxygenation and nutrient delivery to the fetus, resulting in poor urine production and often intrauterine growth restriction (IUGR):
  • Maternal vascular disease:
    • Preeclampsia Preeclampsia A complication of pregnancy, characterized by a complex of symptoms including maternal hypertension and proteinuria with or without pathological edema. Symptoms may range between mild and severe. Pre-eclampsia usually occurs after the 20th week of gestation, but may develop before this time in the presence of trophoblastic disease. Hypertensive Pregnancy Disorders
    • Chronic hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension
    • Pregestational diabetes Diabetes Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus
    • Collagen Collagen A polypeptide substance comprising about one third of the total protein in mammalian organisms. It is the main constituent of skin; connective tissue; and the organic substance of bones (bone and bones) and teeth (tooth). Connective Tissue: Histology vascular disease
    • Thrombophilias Thrombophilias Hypercoagulable states (also referred to as thrombophilias) are a group of hematologic diseases defined by an increased risk of clot formation (i.e., thrombosis) due to either an increase in procoagulants, a decrease in anticoagulants, or a decrease in fibrinolysis. Hypercoagulable States
  • Placental abnormalities Placental abnormalities Normal placental structure and function are essential for a healthy pregnancy. Some of the most common placental abnormalities include structural anomalies (such as a succenturiate lobe or velamentous cord insertion), implantation anomalies (such as placenta accreta and placenta previa), and functional anomalies (such as placental insufficiency). Placental Abnormalities:
    • Placental thrombosis Thrombosis Formation and development of a thrombus or blood clot in the blood vessel. Epidemic Typhus
    • Chronic partial placental abruption Placental Abruption Premature separation of the normally implanted placenta from the uterus. Signs of varying degree of severity include uterine bleeding, uterine muscle hypertonia, and fetal distress or fetal death. Antepartum Hemorrhage
• Fetal anomalies affecting urine production:
  • Polycystic kidney disease
  • Renal agenesis Agenesis Teratogenic Birth Defects
  • Obstructive lesions (e.g., posterior urethral valves, urethral atresia Atresia Hypoplastic Left Heart Syndrome (HLHS))
• Maternal use of certain medications affecting renal blood flow Renal blood flow The amount of the renal blood flow that is going to the functional renal tissue, i.e., parts of the kidney that are involved in production of urine. Glomerular Filtration:
  • ACE inhibitors ACE inhibitors Truncus Arteriosus
  • Prostaglandin synthase inhibitors (e.g., NSAIDs NSAIDS Primary vs Secondary Headaches)
• Twin-twin transfusion syndrome:
  • Vascular anastomoses between 2 placentas, typically in monochorionic diamniotic twins, resulting in unequal blood flow Blood flow Blood flow refers to the movement of a certain volume of blood through the vasculature over a given unit of time (e.g., mL per minute). Vascular Resistance, Flow, and Mean Arterial Pressure
  • Blood is siphoned from one twin to the other resulting in:
    • A growth-restricted “donor twin” with oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios and at risk for severe anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types
    • A “recipient twin” with polyhydramnios Polyhydramnios Polyhydramnios is a pathological excess of amniotic fluid. Common causes of polyhydramnios include fetal anomalies, gestational diabetes, multiple gestations, and congenital infections. Patients are often asymptomatic but may present with dyspnea, extremity swelling, or abdominal distention. Polyhydramnios and at risk for fetal hydrops Hydrops Cholecystitis (a form of heart failure Heart Failure A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction. Total Anomalous Pulmonary Venous Return (TAPVR))
• Other etiologies associated with oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios:
  • Fetal chromosomal abnormalities
  • Maternal infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease:
    • Toxoplasmosis Toxoplasmosis Toxoplasmosis is an infectious disease caused by Toxoplasma gondii, an obligate intracellular protozoan parasite. Felines are the definitive host, but transmission to humans can occur through contact with cat feces or the consumption of contaminated foods. The clinical presentation and complications depend on the host’s immune status. Toxoplasma/Toxoplasmosis, other agents, rubella Rubella An acute infectious disease caused by the rubella virus. The virus enters the respiratory tract via airborne droplet and spreads to the lymphatic system. Rubella Virus, cytomegalovirus Cytomegalovirus CMV is a ubiquitous double-stranded DNA virus belonging to the Herpesviridae family. CMV infections can be transmitted in bodily fluids, such as blood, saliva, urine, semen, and breast milk. The initial infection is usually asymptomatic in the immunocompetent host, or it can present with symptoms of mononucleosis. Cytomegalovirus, and herpes simplex Herpes Simplex A group of acute infections caused by herpes simplex virus type 1 or type 2 that is characterized by the development of one or more small fluid-filled vesicles with a raised erythematous base on the skin or mucous membrane. It occurs as a primary infection or recurs due to a reactivation of a latent infection. Congenital TORCH Infections (TORCH) infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease
    • Parvovirus B19 Parvovirus B19 Primate erythroparvovirus 1 (generally referred to as parvovirus B19, B19 virus, or sometimes erythrovirus B19) ranks among the smallest DNA viruses. Parvovirus B19 is of the family Parvoviridae and genus Erythrovirus. In immunocompetent humans, parvovirus B19 classically results in erythema infectiosum (5th disease) or “slapped cheek syndrome.” Parvovirus B19
  • Fetal demise

Clinical Presentation and Diagnosis

Clinical presentation^[5,7,9]

• ↓ Uterine size for gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care (measured as the “fundal height” at prenatal visits)
• ↓ or inconsistent fetal movements
• Complaints of leaking fluid/ PROM PROM Prelabor rupture of membranes (PROM), previously known as premature rupture of membranes, refers to the rupture of the amniotic sac before the onset of labor. Prelabor rupture of membranes may occur in term or preterm pregnancies. Prelabor Rupture of Membranes
• Incidental finding in routine ultrasound examination (frequent)

History^[5,7,9]

The following should be elicited from an individual’s medical history:

• History of conditions associated with vascular disease
• Medication use
• History of recent infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease

Physical examination^[5,8]

• Fundal heights should be measured at each prenatal visit → poor fundal growth should be investigated further with ultrasound
  • To measure fundal height (FH):^[8]
    • Use a flexible tape measure.
    • Measure from the pubic symphysis Pubic Symphysis A slightly movable cartilaginous joint which occurs between the pubic bones. Vagina, Vulva, and Pelvic Floor: Anatomy to the top of the fundus Fundus The superior portion of the body of the stomach above the level of the cardiac notch. Stomach: Anatomy ( bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess should be empty).
    • The measurement is taken in centimeters.
    • The gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care in weeks should be approximately equal to the FH (e.g., a fetus at 25 weeks’ gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care should have an FH of approximately 25 cm).
• Rule out ruptured membranes (speculum exam for pooling, fern test, pH pH The quantitative measurement of the acidity or basicity of a solution. Acid-Base Balance test of vaginal secretions).
• Look for signs of maternal infection (e.g., fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, rashes Rashes Rashes are a group of diseases that cause abnormal coloration and texture to the skin. The etiologies are numerous but can include irritation, allergens, infections, or inflammatory conditions. Rashes that present in only 1 area of the body are called localized rashes. Generalized rashes occur diffusely throughout the body. Generalized and Localized Rashes).

Imaging: ultrasound^[1,3,4,11]

Amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity can be assessed quantitatively and qualitatively with ultrasound. For diagnosis, quantitative assessment is recommended by measuring AFI and/or SDP. 

• AFI:
  • Calculation: Divide the uterus Uterus The uterus, cervix, and fallopian tubes are part of the internal female reproductive system. The uterus has a thick wall made of smooth muscle (the myometrium) and an inner mucosal layer (the endometrium). The most inferior portion of the uterus is the cervix, which connects the uterine cavity to the vagina. Uterus, Cervix, and Fallopian Tubes: Anatomy into 4 quadrants, measure the largest vertical pocket of fluid in each quadrant, and add the values together.^[3]
    • The pockets of fluid must be ≥ 1 cm wide and free of umbilical cord Umbilical cord The flexible rope-like structure that connects a developing fetus to the placenta in mammals. The cord contains blood vessels which carry oxygen and nutrients from the mother to the fetus and waste products away from the fetus. Placenta, Umbilical Cord, and Amniotic Cavity and fetal parts.
    • The probe Probe A device placed on the patient’s body to visualize a target Ultrasound (Sonography) should be held perpendicular to either the ground or the uterine wall.
  • Normal AFI: > 5 cm and < 24 cm
  • Oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios: ≤ 5 cm 
• SDP (also called the deepest vertical pocket (DVP) or maximum vertical pocket ( MVP MVP Mitral valve prolapse (MVP) is the most common cardiac valvular defect, and is characterized by bulging of the mitral valve (MV) cusps into the left atrium (LA) during systole. Mitral valve prolapse is most commonly due to idiopathic myxomatous degeneration. Patients are typically asymptomatic. Mitral Valve Prolapse)):
  • The vertical dimension of the largest pocket of amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity; the SDP cannot include the umbilical cord Umbilical cord The flexible rope-like structure that connects a developing fetus to the placenta in mammals. The cord contains blood vessels which carry oxygen and nutrients from the mother to the fetus and waste products away from the fetus. Placenta, Umbilical Cord, and Amniotic Cavity or fetal parts
  • Normal SDP: ≥ 2 cm and < 8 cm
  • Oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios: < 2 cm^[3]

Follow-up testing^[1,3,11]

If a patient is diagnosed with oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios, additional testing may be indicated to identify the underlying etiology:

• Ultrasound to assess fetal growth:
  • Always indicated
  • IUGR points to uteroplacental insufficiency Uteroplacental Insufficiency Uteroplacental insufficiency may be acute or chronic and refers to the inability of the placenta to deliver a sufficient supply of O2 and nutrients to the fetus Placental Abnormalities 
• Fetal anatomical survey via ultrasound (if not already done) to look for fetal anomalies
• Maternal screening Screening Preoperative Care for aneuploidy:
  • Several combinations of ultrasound and serum markers exist as screening Screening Preoperative Care tests (e.g., the “ quad screen Quad Screen Prenatal Care”)
  • Noninvasive prenatal testing (NIPT): screen for fetal DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure fragments in maternal blood
  • Amniocentesis Amniocentesis Percutaneous transabdominal puncture of the uterus during pregnancy to obtain amniotic fluid. It is commonly used for fetal karyotype determination in order to diagnose abnormal fetal conditions. Polyhydramnios: an invasive sampling Invasive sampling Coccidioides/Coccidioidomycosis of amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity (contains fetal DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure) to test for genetic anomalies
• If suspicion arises based on the clinical picture, test maternal serum and amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity for TORCH pathogens.

Management

Antenatal management^[1,3,4,6]

• No effective long-term treatment for oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios is available.
• Encourage maternal hydration:
  • The goal is to ↑ uteroplacental perfusion.
  • Oral hydration is superior to IV hydration Iv Hydration Crush Syndrome.
  • Results are typically transient, but still may provide some benefits.
• Monitor regularly to ensure continued fetal well-being.
• Monitoring techniques:
  • Fetal “kick counting” by the mother: The mother should feel 10 movements in a 2-hour time period at least 1x/day.
  • Outpatient antepartum fetal surveillance Surveillance Developmental Milestones and Normal Growth options:^[1]
    • Fetal nonstress test (NST): monitors fetal heart rate Heart rate The number of times the heart ventricles contract per unit of time, usually per minute. Cardiac Physiology and uterine contractions for 20 minutes
    • Biophysical profile Biophysical Profile Obstetric Imaging (BPP): an obstetric ultrasound to identify certain types of fetal movements (includes a fluid measurement)
    • Modified BPP: an NST + SDP
• Once oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios is diagnosed, antepartum fetal surveillance Surveillance Developmental Milestones and Normal Growth is typically performed 1–2 times per week (based on formal guidance from the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) in the United States).^[1]
• Therapies under investigation to treat true oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios in the 2nd trimester:
  • Serial abdominal amnioinfusions: A needle is inserted into the amniotic cavity Amniotic cavity Embryoblast and Trophoblast Development under ultrasound guidance (similar to an amniocentesis Amniocentesis Percutaneous transabdominal puncture of the uterus during pregnancy to obtain amniotic fluid. It is commonly used for fetal karyotype determination in order to diagnose abnormal fetal conditions. Polyhydramnios) and fluid is instilled.^[5,10,12]
  • Fetal vesicoamniotic shunt: A surgical shunt is created in fetuses with oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios due to lower urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract: Anatomy obstructions (e.g., peripheral urethral valves), relieving pressure on the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy and improving the oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios.^[5,6]

Delivery^[1,2,10,12]

• Delivery is typically indicated:
  • After 36–37 weeks’ gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care (regardless of etiology), or earlier for etiology-specific indications^[2]
  • At 34 weeks’ gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care for patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with preterm prelabor rupture of membranes Prelabor Rupture of Membranes Prelabor rupture of membranes (PROM), previously known as premature rupture of membranes, refers to the rupture of the amniotic sac before the onset of labor. Prelabor rupture of membranes may occur in term or preterm pregnancies. Prelabor Rupture of Membranes (PPROM)
  • If monitoring is nonreassuring
• Route of delivery:
  • Vaginal deliveries are preferred if patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship are candidates.
  • Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship should be carefully monitored (typically with continuous cardiotocography) in labor for signs of fetal distress.
  • Cesarean or operative vaginal deliveries should be performed for typical obstetric indications, including nonreassuring intrapartum fetal monitoring Fetal monitoring The primary goals of antepartum testing and monitoring are to assess fetal well-being, identify treatable situations that may cause complications, and evaluate for chromosomal abnormalities. These tests are divided into screening tests (which include cell-free DNA testing, serum analyte testing, and nuchal translucency measurements), and diagnostic tests, which provide a definitive diagnosis of aneuploidy and include chorionic villus sampling (CVS) and amniocentesis. Antepartum Testing and Monitoring.
• Amnioinfusion Amnioinfusion Oligohydramnios:
  • Once membranes are ruptured, a thin catheter can be inserted into the uterine cavity and fluid instilled to “refill” the amniotic cavity Amniotic cavity Embryoblast and Trophoblast Development.
  • May be helpful when monitoring indicates fetal stress from repetitive compression Compression Blunt Chest Trauma of the umbilical cord Umbilical cord The flexible rope-like structure that connects a developing fetus to the placenta in mammals. The cord contains blood vessels which carry oxygen and nutrients from the mother to the fetus and waste products away from the fetus. Placenta, Umbilical Cord, and Amniotic Cavity (seen on the monitor as variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables decelerations)
  • The catheter also serves as an intrauterine pressure catheter (IUPC), which is capable of measuring the strength of uterine contractions (helpful in managing inductions of labor).
  • Approximately 200–300 mL of sterile Sterile Basic Procedures saline is typically instilled.

Prognosis and Complications

The fetal/neonatal prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas depends on the cause, severity, gestational age Gestational age The age of the conceptus, beginning from the time of fertilization. In clinical obstetrics, the gestational age is often estimated as the time from the last day of the last menstruation which is about 2 weeks before ovulation and fertilization. Pregnancy: Diagnosis, Physiology, and Care at diagnosis, and duration of oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios.

First trimester^[5,7,9]

• Ominous finding typically ending with spontaneous abortion Abortion Expulsion of the product of fertilization before completing the term of gestation and without deliberate interference. Spontaneous Abortion (94%)
• Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship should be counseled regarding the probability Probability Probability is a mathematical tool used to study randomness and provide predictions about the likelihood of something happening. There are several basic rules of probability that can be used to help determine the probability of multiple events happening together, separately, or sequentially. Basics of Probability and signs of miscarriage Miscarriage Spontaneous abortion, also known as miscarriage, is the loss of a pregnancy before 20 weeks’ gestation. However, the layperson use of the term “abortion” is often intended to refer to induced termination of a pregnancy, whereas “miscarriage” is preferred for spontaneous loss. Spontaneous Abortion.
• Serial ultrasound exams should be done to follow the natural history of the process.
• No treatments are available.

Second trimester^[5,7,9]

• Pregnancies with borderline or low–normal amniotic fluid Amniotic fluid A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis). Placenta, Umbilical Cord, and Amniotic Cavity volume generally have a good prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas:
  • Obtain serial sonographic examinations to assess the progress of the disease.
  • Emphasize maternal hydration and avoidance of NSAIDs NSAIDS Primary vs Secondary Headaches.
• True oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios typically has a poor prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas.
• Survival rates based on etiology:
  • PPROM: 21%
  • Placental abruption Placental Abruption Premature separation of the normally implanted placenta from the uterus. Signs of varying degree of severity include uterine bleeding, uterine muscle hypertonia, and fetal distress or fetal death. Antepartum Hemorrhage: 22%
  • Idiopathic Idiopathic Dermatomyositis: 20%
  • Congenital Congenital Chorioretinitis anomalies: 1.5%
  • Fetal growth restriction Fetal growth restriction Fetal growth restriction (FGR), also known as intrauterine fetal growth restriction (IUGR), is an estimated fetal weight (EFW) or abdominal circumference < 10th percentile for gestational age. The term small for gestational age (SGA) is sometimes erroneously used interchangeably with FGR. Fetal Growth Restriction: 0%
  • Overall survival rate: 10%
• Pulmonary hypoplasia Hypoplasia Hypoplastic Left Heart Syndrome (HLHS) is typically the cause of death because little can be done to support respiration Respiration The act of breathing with the lungs, consisting of inhalation, or the taking into the lungs of the ambient air, and of exhalation, or the expelling of the modified air which contains more carbon dioxide than the air taken in. Nose Anatomy (External & Internal) in the infant after delivery.
• Limb contractures Contractures Prolonged shortening of the muscle or other soft tissue around a joint, preventing movement of the joint. Wound Healing are common due to long-standing compression Compression Blunt Chest Trauma.
• Depending on the clinical situation (e.g., severe oligohydramnios Oligohydramnios Oligohydramnios refers to amniotic fluid volume less than expected for the current gestational age. Oligohydramnios is diagnosed by ultrasound and defined as an amniotic fluid index (AFI) of ‰¤ 5 cm or a single deep pocket (SDP) of < 2 cm in the 2nd or 3rd trimester. Oligohydramnios due to an anomaly identified on an 18-week anatomy scan), elective termination may be an appropriate option.

Third trimester^[5,7,9]

• Typically a better prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas when diagnosed in the 3rd trimester due to more developed respiratory and renal organs
• Adverse outcomes are related to:
  • Umbilical cord Umbilical cord The flexible rope-like structure that connects a developing fetus to the placenta in mammals. The cord contains blood vessels which carry oxygen and nutrients from the mother to the fetus and waste products away from the fetus. Placenta, Umbilical Cord, and Amniotic Cavity compression Compression Blunt Chest Trauma
  • Uteroplacental insufficiency Uteroplacental Insufficiency Uteroplacental insufficiency may be acute or chronic and refers to the inability of the placenta to deliver a sufficient supply of O2 and nutrients to the fetus Placental Abnormalities
  • Meconium aspiration Meconium Aspiration A condition caused by inhalation of meconium into the lung of fetus or newborn, usually due to vigorous respiratory movements during difficult parturition or respiratory system abnormalities. Meconium aspirate may block small airways leading to difficulties in pulmonary gas exchange and aspiration pneumonia. Physical Examination of the Newborn
• Overall survival rate: > 85%

Neonatal complications^[5,7,9]

• Premature Premature Childbirth before 37 weeks of pregnancy (259 days from the first day of the mother’s last menstrual period, or 245 days after fertilization). Necrotizing Enterocolitis birth
• Pulmonary hypoplasia Hypoplasia Hypoplastic Left Heart Syndrome (HLHS)
• IUGR
• Cord compression Compression Blunt Chest Trauma
• Meconium aspiration Meconium Aspiration A condition caused by inhalation of meconium into the lung of fetus or newborn, usually due to vigorous respiratory movements during difficult parturition or respiratory system abnormalities. Meconium aspirate may block small airways leading to difficulties in pulmonary gas exchange and aspiration pneumonia. Physical Examination of the Newborn
• Deformities due to intraamniotic adhesions or compression Compression Blunt Chest Trauma:
  • Arthrogryposis ( contractures Contractures Prolonged shortening of the muscle or other soft tissue around a joint, preventing movement of the joint. Wound Healing of multiple joints)
  • Alteration in the shape of the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy
  • Torticollis Torticollis A symptom, not a disease, of a twisted neck. In most instances, the head is tipped toward one side and the chin rotated toward the other. The involuntary muscle contractions in the neck region of patients with torticollis can be due to congenital defects, trauma, inflammation, tumors, and neurological or other factors. Cranial Nerve Palsies (i.e. wry neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess)
  • Club foot Foot The foot is the terminal portion of the lower limb, whose primary function is to bear weight and facilitate locomotion. The foot comprises 26 bones, including the tarsal bones, metatarsal bones, and phalanges. The bones of the foot form longitudinal and transverse arches and are supported by various muscles, ligaments, and tendons. Foot: Anatomy
  • Amputation Amputation An amputation is the separation of a portion of the limb or the entire limb from the body, along with the bone. Amputations are generally indicated for conditions that compromise the viability of the limb or promote the spread of a local process that could manifest systemically. Amputation of the limb
• Compression Compression Blunt Chest Trauma of fetal organs leading to hypoxic-ischemic encephalopathy Encephalopathy Hyper-IgM Syndrome (HIE)