This presentation is consistent with polyhydramnios, an excess of amniotic fluid. Polyhydramnios can occur secondary to gastrointestinal obstruction such as duodenal atresia.
Polyhydramnios is often defined as amniotic fluid exceeding 1.5-2 L or an AFI greater than 20-25. Excess amniotic fluid is generally caused by either decreased resorption (decreased fetal swallowing) or increased production (excess fetal urination). As mentioned above, gastrointestinal obstruction is a common cause of decreased resorption of amniotic fluid; associated abnormalities include intestinal atresia, tracheoesophageal fistula, or anencephaly. Additionally, fetal polyuria, as in maternal diabetes, leads to increased amniotic fluid.
Deutchman and Sakornbut discussed the utility of diagnostic ultrasound in the peri-partum setting. Ultrasound is useful for amniotic fluid assessment among numerous other benefits, including determination of fetal number, fetal lie/presentation, and placental location.
Morris et al. evaluated using amniotic fluid measurement as a predictor of pregnancy/fetal outcomes. They concluded that oligohydramnios is strongly associated with fetal size small for gestational age and mortality, whereas polyhydramnios is associated with birthweight greater than the 90th percentile. Despite these associations, the authors concluded that amniotic fluid measurement does not accurately predict outcomes for individuals.
Illustration A is an ultrasound showing excess amniotic fluid; the largest pocket of fluid in this image measures 11 cm (classified as moderate polyhydramnios). Illustration B shows a diagram of Potter's syndrome (associated with oligohydramnios) and its sequelae. Illustration C shows percentiles associated with amniotic fluid volume by gestational age.
Answer 1: Renal agenesis leads to decreased fetal urine production and therefore oligohydramnios.
Answer 2: Pulmonary hypoplasia is a complication of oligohydramnios; this is known as Potter's syndrome.
Answer 4: Decreased fetal urination, such as is seen in male fetuses with posterior urethral valves, leads to oligohydramnios and subsequently Potter's syndrome.
Answer 5: Juvenile polycystic kidney disease is associated with decreased fetal urination and oligohydramnios.
Deutchman ME, Sakornbut EL. Diagnostic ultrasound in labor and delivery. Am Fam Physician. 1995 Jan;51(1):145-54.
PMID:7810467 (Link to Abstract)
Morris RK, Meller CH, Tamblyn J, Malin GM, Riley RD, Kilby MD, Robson SC, Khan KS. Association and prediction of amniotic fluid measurements for adverse pregnancy outcome: systematic review and meta-analysis. BJOG. 2014 May;121(6):686-99.
PMID:24738894 (Link to Abstract)
USMLE World Step 1 QBank Question #337. Copyright © USMLEWorld, LLC 2012