Severe Polyhydramnios Associated With Antenatal Bartter Syndrome.

Polyhydramnios is defined as an abnormal increase in amniotic fluid volume and is most commonly diagnosed during the second or third trimester of pregnancy. Although the majority of cases are idiopathic, polyhydramnios may also be associated with maternal conditions, fetal structural anomalies, and rare genetic disorders. We present the case of a 35-year-old G3P1102 patient at 27 weeks and 2 days of gestation who presented with preterm premature rupture of membranes (PPROM) and preterm labor. Obstetric ultrasonography demonstrated severe polyhydramnios with an amniotic fluid index (AFI) of 57.66 cm in the setting of a structurally normal fetus. In the postnatal period, the neonate developed brisk diuresis and electrolyte abnormalities, raising clinical suspicion for antenatal Bartter syndrome. Additional neonatal evaluation demonstrated renal salt wasting and hypercalciuria, findings supportive of this diagnosis. This case highlights the importance of considering antenatal Bartter syndrome in the differential diagnosis of severe unexplained polyhydramnios, particularly in the setting of a structurally normal fetus, as early recognition may facilitate perinatal planning and potentially improve neonatal outcomes.