Overview

Definition

Polyhydramnios is an abnormally high level of amniotic fluid in the amniotic sac.

Epidemiology

• Incidence range: 0.2%–1.6%
• Identification is often incidental during the 3rd trimester.
• Polyhydramnios is idiopathic in 60%–70% of cases.
• 20% of cases are due to congenital anomalies.

Etiology

• Idiopathic
• Fetal anomalies:
  • Gastrointestinal:
    • Esophageal atresia Esophageal atresia Esophageal atresia is a congenital anomaly in which the upper esophagus is separated from the lower esophagus and ends in a blind pouch. The condition may be isolated or associated with tracheoesophageal fistula, which is an abnormal connection between the trachea and esophagus. Esophageal Atresia and Tracheoesophageal Fistula
    • Duodenal atresia
    • Intestinal obstruction
  • CNS:
    • Anencephaly
    • Dandy-Walker malformation
  • Pulmonary:
    • Diaphragmatic hernia
    • Congenital pulmonary airway obstruction Airway obstruction Airway obstruction is a partial or complete blockage of the airways that impedes airflow. An airway obstruction can be classified as upper, central, or lower depending on location. Lower airway obstruction (LAO) is usually a manifestation of chronic disease, such as asthma or chronic obstructive pulmonary disease (COPD). Airway Obstruction
  • Neuromuscular:
    • Fetal akinesia deformation sequence
    • Skeletal dysplasia
• Fetal chromosomal abnormalities:
  • Trisomy 18 Trisomy 18 Edwards syndrome, or trisomy 18, is a genetic syndrome caused by the presence of an extra chromosome 18. The extra chromosome is either from 3 full copies of chromosome 18 or an additional segment of chromosome 18. As the 2nd most common trisomy, Edwards syndrome is seen in 1 out of every 5,500 live births. Edwards Syndrome (Trisomy 18)
  • Trisomy 21
• Fetal 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:
  • Alloimmunization
  • Congenital infection (e.g., parvovirus)
  • Fetomaternal hemorrhage
• Hydrops fetalis
• Twin-to-twin transfusion syndrome
• Gestational diabetes
• Maternal uremia
• Maternal hypercalcemia Hypercalcemia Hypercalcemia (serum calcium > 10.5 mg/dL) can result from various conditions, the majority of which are due to hyperparathyroidism and malignancy. Other causes include disorders leading to vitamin D elevation, granulomatous diseases, and the use of certain pharmacological agents. Symptoms vary depending on calcium levels and the onset of hypercalcemia. Hypercalcemia
• Fetal and placental tumors
• Intrapartum infections (e.g., TORCH infections TORCH infections Congenital infections are acquired in utero or during passage through the birth canal at birth and can be associated with significant morbidity and mortality for the infant. The TORCH infections are a group of congenital infections grouped due to their similar presentation. The acronym TORCH arises from the names of the infectious agents that cause the diseases included in this group: toxoplasmosis, other agents (syphilis, varicella zoster virus (VZV), parvovirus B19, and HIV), rubella, CMV, and herpes simplex. Congenital TORCH Infections)
• Maternal intake of lithium

Pathophysiology

Normal physiologic conditions:

• Amniotic fluid is derived from fetal urination.
• Fluid absorption Absorption Absorption involves the uptake of nutrient molecules and their transfer from the lumen of the GI tract across the enterocytes and into the interstitial space, where they can be taken up in the venous or lymphatic circulation. Digestion and Absorption occurs through fetal swallowing.
• Equilibrium develops between the production and excretion of amniotic fluid.

Two major causes of polyhydramnios:

1. Increased fetal urination:
   • High cardiac output (fetal 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)
   • Volume overload (twin-to-twin transfusion syndrome)
   • Osmotic diuresis (maternal diabetes, maternal uremia)
2. Decreased fetal swallowing

Clinical Presentation

• Most patients are asymptomatic with polyhydramnios an incidental finding on ultrasound.
• Symptomatic patients may have:
  • Dyspnea
  • Extremity edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema
  • Constipation Constipation Constipation is common and may be due to a variety of causes. Constipation is generally defined as bowel movement frequency < 3 times per week. Patients who are constipated often strain to pass hard stools. The condition is classified as primary (also known as idiopathic or functional constipation) or secondary, and as acute or chronic. Constipation
  • Abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
  • Tightness of the abdominal wall
  • Rapidly enlarging abdomen
  • Decreased fetal movement
• The baby is often in breech presentation.

Diagnosis

History

• Often unhelpful
• Focus on the presence of risk factors (e.g., diabetes, genetic diseases).
• Ask about the maternal perception of fetal movement (often decreased).

Physical exam

• Assessments:
  • Abdominal size and tightness
  • Lower extremity edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema
• Measurement of fundal height (> 3 cm above gestational age is suspicious):
  • Use a flexible tape measure.
  • Measure from the pubic symphysis to the top of the fundus.
  • Measure in centimeters.
  • The age of gestation is associated with the measurement between 16–36 weeks (e.g., 25 weeks is 25 cm).

Diagnostic testing

• Amniotic fluid assessment with ultrasound:
  • 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. Posterior Abdominal Wall into 4 quadrants.
  • Measure the amniotic fluid vertically.
  • Amniotic fluid index (AFI):
    • A sum of the deepest amniotic pocket in all 4 quadrants
    • Values between 8–18 cm are normal.
  • Single deep pocket (SDP):
    • Amniotic fluid volume in the deepest pocket
    • Values between 2–8 cm are normal.
• Fetal organ screening
• Middle cerebral artery peak systolic velocity measurement: 
  • Measured by ultrasound
  • ↑ Value indicates fetal 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
• Amniocentesis:
  • Fetal karyotyping for trisomy 21, 13, and 18
  • PCR PCR Polymerase chain reaction (PCR) is a technique that amplifies DNA fragments exponentially for analysis. The process is highly specific, allowing for the targeting of specific genomic sequences, even with minuscule sample amounts. The PCR cycles multiple times through 3 phases: denaturation of the template DNA, annealing of a specific primer to the individual DNA strands, and synthesis/elongation of new DNA molecules. Polymerase Chain Reaction (PCR) for detection of congenital infections
  • Dye dilution technique:
    • The gold standard to test the amniotic fluid measurement
    • Rarely done
• Other:
  • Glucose tolerance test
  • Screening for congenital infections:
    • TORCH
    • HIV
    • Hepatitis
  • Maternal blood type
  • Rhesus factor
  • Screening for antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins (Kell, Duffy, D, and C)
  • Lithium levels
  • Kleihauer-Betke test: evaluates fetal-maternal hemorrhage
  • Hemoglobin Barts (significant in Asian descent): may be heterozygous for α- thalassemia Thalassemia Thalassemia is a hereditary cause of microcytic hypochromic anemia and results from a deficiency in either the α or β globin chains, resulting in hemoglobinopathy. The presentation of thalassemia depends on the number of defective chains present and can range from being asymptomatic to rendering the more severely affected patients to be transfusion dependent. Thalassemia

Management

Prenatal care Prenatal care Prenatal care is a systematic and periodic assessment of pregnant women during gestation to assure the best health outcome for the mother and her fetus. Prenatal care prevents and identifies maternal and fetal problems that adversely affect the pregnancy outcome. Prenatal Care

• Treatment is dependent on the severity of polyhydramnios.
• No treatment is required for mild forms of polyhydramnios.
• Maternal-fetal counseling is recommended.
• Serial ultrasound is performed to assess fetal growth and AFI.
• Bed rest to ↓ the likelihood of preterm labor Preterm labor Preterm labor refers to regular uterine contractions leading to cervical change prior to 37 weeks of gestation; preterm birth refers to birth prior to 37 weeks of gestation. Preterm birth may be spontaneous due to preterm labor, preterm prelabor rupture of membranes (PPROM), or cervical insufficiency. Preterm Labor and Birth
• Severe polyhydramnios is treated with:
  • Amnioreduction: Serial AFI monitoring is recommended every 1–3 weeks after the procedure.
  • Prostaglandin synthetase inhibitors: stimulation of fetal ADH secretion → ↓ of renal blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure → ↓ diuresis
  • Sulindac
• Genetic counseling
• Intrauterine blood transfusion (fetal 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)
• Laser photocoagulation (twin-to-twin transfusion syndrome)

Delivery

• Labor induction is not clearly indicated.
• Continuous 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 is recommended.
• Use steroids to enhance fetal lung maturity if preterm delivery is anticipated.
• Controlled induction can be performed at 38 weeks of gestation for:
  • Severe polyhydramnios
  • Fetal abnormalities

Complications

• Preterm labor Labor Labor is the normal physiologic process defined as uterine contractions resulting in dilatation and effacement of the cervix, which culminates in expulsion of the fetus and the products of conception. Normal and Abnormal Labor
• Premature rupture of membranes
• Postpartum hemorrhage Postpartum hemorrhage Postpartum hemorrhage is one of the most common and deadly obstetric complications. Since 2017, postpartum hemorrhage has been defined as blood loss greater than 1,000 mL for both cesarean and vaginal deliveries, or excessive blood loss with signs of hemodynamic instability. Postpartum Hemorrhage
• Fetal malposition
• Umbilical cord prolapse
• Fetal death

Differential Diagnosis

• Preeclampsia: a condition characterized by new-onset 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 after 20 weeks of gestation, and proteinuria or signs of end-organ damage. Patients present with visual abnormalities, headache, shortness of breath, and epigastric pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain. Diagnosis is based on new-onset 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 and the presence of proteinuria or end-organ damage. Management includes the administration of antihypertensives and possibly labor Labor Labor is the normal physiologic process defined as uterine contractions resulting in dilatation and effacement of the cervix, which culminates in expulsion of the fetus and the products of conception. Normal and Abnormal Labor induction.
• Placental abruption: the placenta Placenta The placenta consists of a fetal side and a maternal side, and it provides a vascular communication between the mother and the fetus. This communication allows the mother to provide nutrients to the fetus and allows for removal of waste products from fetal blood. Placenta, Umbilical Cord, and Amniotic Cavity prematurely separates from the inner lining of 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. Posterior Abdominal Wall. Placental abruption is a dangerous complication of pregnancy Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-HCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care. Patients often present with painful vaginal bleeding, uterine contractions, abdominal or back pain Back pain Back pain is a common complaint among the general population and is mostly self-limiting. Back pain can be classified as acute, subacute, or chronic depending on the duration of symptoms. The wide variety of potential etiologies include degenerative, mechanical, malignant, infectious, rheumatologic, and extraspinal causes. Back Pain, and premature birth. Management depends on gestational age and hemodynamic status of the mother and fetus. Placental abruption includes inpatient admission of the patient and possibly delivery. 
• Congestive heart failure Congestive heart failure Congestive heart failure refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. Congestive Heart Failure: the heart is unable to pump enough blood to meet the metabolic requirements of the body. Patients often present with exertional dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, chest pain Chest Pain Chest pain is one of the most common and challenging complaints that may present in an inpatient and outpatient setting. The differential diagnosis of chest pain is large and includes cardiac, gastrointestinal, pulmonary, musculoskeletal, and psychiatric etiologies. Chest Pain, paroxysmal nocturnal dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, and abdominal distention due to ascites Ascites Ascites is the pathologic accumulation of fluid within the peritoneal cavity that occurs due to an osmotic and/or hydrostatic pressure imbalance secondary to portal hypertension (cirrhosis, heart failure) or non-portal hypertension (hypoalbuminemia, malignancy, infection). Ascites and/or hepatomegaly. Echocardiography confirms the diagnosis. Management includes sodium restriction, administration of diuretics, inotropic agents, and vasodilators.