A 32-year-old woman comes to the office at 28 weeks gestation due to dyspnea. She has been feeling short of breath when she is supine but has no other symptoms. The patient has had no prenatal care during her pregnancy. She has a history of epilepsy that is well-controlled with medication. She lives with her husband and does not use tobacco, alcohol, or illicit drugs. Her immunizations are up to date, and she has no allergies. Physical examination shows a uterine size that is larger than expected for gestational age. Sonographic assessment shows markedly elevated amniotic fluid levels. Which of the following fetal anomalies would most likely account for this patient's polyhydramnios?

Question

A 32-year-old woman comes to the office at 28 weeks gestation due to dyspnea.  She has been feeling short of breath when she is supine but has no other symptoms. The patient has had no prenatal care during her pregnancy.  She has a history of epilepsy that is well-controlled with medication.  She lives with her husband and does not use tobacco, alcohol, or illicit drugs.  Her immunizations are up to date, and she has no allergies.  Physical examination shows a uterine size that is larger than expected for gestational age.  Sonographic assessment shows markedly elevated amniotic fluid levels.  Which of the following fetal anomalies would most likely account for this patient's polyhydramnios?

Quizplus · Accepted Answer

11ec160b_374e_6b1c_9249_cda7da35d89c_MD0001_00 Polyhydramnios is the excessive accumulation of amniotic fluid. Moderate-to-severe polyhydramnios causes uterine enlargement (eg, increased abdominal circumference) out of proportion to gestational age. Potential complications include preterm labor, placental abruption, and uterine atony due to uterine overdistention. Polyhydramnios also increases the risk of maternal respiratory compromise as the abdominal cavity impairs lung expansion. Polyhydramnios can be due to decreased fetal swallowing or increased fetal urination. Fetal anomalies associated with impaired swallowing include gastrointestinal obstruction (eg, duodenal, esophageal, or intestinal atresia) and anencephaly (a defect of the cranial neural tube). Causes of increased fetal urination include high cardiac output due to anemia or twin-to-twin transfusion syndrome. Maternal diabetes and multiple gestations tend to cause milder polyhydramnios compared to the aforementioned major fetal anomalies. This patient's prenatal use of anti-epileptic therapy (eg, valproate, carbamazepine, phenytoin) is a substantial risk factor for fetal neural tube defects such as anencephaly. Like anencephaly, spina bifida (Choice F) is a group of neural tube defects (eg, occulta, meningocele, myelomeningocele) that can result from maternal folic acid deficiency and use of folic acid antagonists (anti-epileptic drugs, trimethoprim). However, spina bifida occulta, the mildest form, is not associated with polyhydramnios as fetal swallowing of amniotic fluid remains normal. (Choice B) Atrial septal defects (ASDs) are one of the most common congenital heart diseases. ASDs are usually asymptomatic in utero. The diagnosis is usually made after birth based on wide fixed splitting of S2 on physical examination. ASDs are not associated with polyhydramnios. (Choices C, D, and E) Renal agenesis is associated with severe oligohydramnios (too little amniotic fluid) after 16 weeks of gestation when the majority of the amniotic fluid is derived from fetal urine. Posterior urethral valves in male fetuses can also result in decreased fetal urine output and oligohydramnios. Oligohydramnios, in turn, can lead to excessive fetal compression causing flat facies and limb deformity (ie, Potter sequence). Pulmonary hypoplasia is a consequence of oligohydramnios and is not associated with polyhydramnios. Educational objective: Polyhydramnios (excessive accumulation of amniotic fluid) presents with increased abdominal circumference out of proportion to gestational age. The etiology is decreased fetal swallowing or increased fetal urination. Fetal anomalies associated with impaired swallowing include gastrointestinal obstruction (eg, duodenal, esophageal, or intestinal atresia) and anencephaly.

A 32-Year-Old Woman Comes to the Office at 28 Weeks