A 36-year-old woman, gravida 1 para 0, at 34 weeks gestation comes to the emergency department due to 4 hours of decreased fetal movement. She has had no vaginal bleeding, contractions, or leakage of fluid. The patient reports no headaches, changes in vision, or right upper quadrant pain. Her last prenatal visit was at 16 weeks gestation; she moved from out of state at 18 weeks gestation for a new job. A maternal serum alpha-fetoprotein level performed at that visit was normal. The patient has a history of chronic back pain for which she takes a daily nonsteroidal anti-inflammatory drug. She has had no surgeries. The patient does not use tobacco, alcohol, or illicit drugs. Blood pressure is 160/90 mm Hg and pulse is 68/min. BMI is 30 kg/m². Fetal heart rate shows a baseline of 140/min, moderate variability, accelerations, and no decelerations. The tocometer shows no contractions. Fundal height is 38 cm. Bedside ultrasound reveals an estimated fetal weight consistent with 36 weeks gestation and an amniotic fluid index of 30 cm. Laboratory results are as follows: Which of the following is the most likely cause of this patient's ultrasound findings?

Question

Quizplus · Accepted Answer

Explanation: 11ec2b69_c032_39b4_8f63_c17b356b8f4c_MD0005_00 The amniotic fluid index (AFI) is a component of antepartum fetal surveillance that measures the amniotic fluid volume surrounding the fetus. Amniotic fluid is produced by the fetal kidneys and lungs and is removed by fetal swallowing and transplacental fluid reabsorption. The AFI helps to evaluate fetal well-being, as normal levels (5-23 cm) suggest normal function of the placenta and fetal kidneys and lungs. Abnormal AFI levels are typically due to impairments in either amniotic fluid production (eg, oligohydramnios) or removal (eg, polyhydramnios). Polyhydramnios, an AFI >24 cm, is typically diagnosed by either routine ultrasound or by ultrasound performed to evaluate a fundal height that is larger than expected for gestational age. Polyhydramnios is associated with an increased risk for maternal complications (eg, respiratory distress from impaired diaphragm movement), obstetric complications (eg, preterm premature rupture of membranes, abruptio placentae, umbilical cord prolapse, postpartum hemorrhage), and adverse fetal outcomes (eg, preterm delivery, macrosomia, neonatal mortality). Although polyhydramnios can be idiopathic, common causes include maternal diabetes mellitus, multiple gestation, and congenital anomalies (eg, duodenal atresia). Poorly controlled (or undiagnosed) diabetes mellitus is associated with fetal hyperglycemia. This hyperglycemia leads to osmotic diuresis, fetal polyuria, and polyhydramnios. The most likely etiology of this patient's polyhydramnios is underlying diabetes mellitus, which is suggested by her large fetus and glucose on urinalysis. (Choice A) Anencephaly can cause polyhydramnios due to an abnormal fetal swallowing reflex that results in the inability to remove amniotic fluid. However, this patient's normal prenatal maternal serum alpha-fetoprotein level makes this diagnosis less likely. Anencephaly (Choice B) Congenital infection (eg, parvovirus) may cause polyhydramnios. However, infection typically presents with a concomitant fetal growth restriction, which is not seen in this patient. (Choice D) Nonsteroidal anti-inflammatory drugs can decrease fetal renal blood flow, which causes fetal oliguria and oligohydramnios. (Choice E) Preeclampsia is typically associated with fetal growth restriction and oligohydramnios due to chronic placental insufficiency. Placental insufficiency causes shunting of fetal blood to the fetal brain and away from the fetal kidneys, decreasing fetal urinary output and causing oligohydramnios. Educational objective: Polyhydramnios, an amniotic fluid index >24 cm, is associated with maternal, obstetric, and fetal complications. Common etiologies of polyhydramnios include maternal diabetes mellitus and congenital anomalies (eg, anencephaly, duodenal atresia). References: Outcome of pregnancy in women diagnosed with idiopathic polyhydramnios. (http://www.ncbi.nlm.nih.gov/pubmed/28251633) Idiopathic polyhydramnios: persistence across gestation and impact on pregnancy outcomes. (http://www.ncbi.nlm.nih.gov/pubmed/26937648)

A 36-Year-Old Woman, Gravida 1 Para 0, at 34 Weeks