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.