Established facts: Bartter syndrome is a rare heterogeneous group of autosomal-recessive salt-losing renal tubular disorders that can present in fetal life (antenatal Bartter syndrome; ABS) as “unexplained” early-onset polyhydramnios, often associated with growth restriction. Prenatal diagnosis of the condition involves assessment of amniotic fluid biochemistry in a setting of polyuric polyhydramnios; with elevated chloride levels considered a consistent and diagnostic finding. Other amniotic fluid biochemical markers have been described, notably increased aldosterone levels, and low total protein levels. Novel insight: Antenatal Bartter syndrome is a heterogeneous group of renal disorders. While certain biochemical features in amniotic fluid might heighten suspicion, final diagnosis can only be made in the postnatal setting. In the setting of unexplained severe polyhydramnios, clinicians should continue to entertain the diagnosis of antenatal Bartter Syndrome and maintain neonatal surveillance, even if amniotic fluid markers do not support the diagnosis.