Fetal gut atresia is variably associated with polyhydramnios. In order to determine which pregnancies will develop polyhydramnios, the case notes of 80 babies with gut atresia and stenosis were reviewed. Maternal polyhydramnios developed in all cases of pure oesophageal atresia (n = 8), all cases of Type III duodenal atresia (DA) with a non-bifid bile duct (n = 8), 80% of cases with type I DA (n = 10), and 24% of atresias of the small intestine (n = 34). Polyhydramnios did not develop in any case where there was not total obstruction except in 1 baby with DA and a bifid bile duct (BBD). These included stenosis of the oesophagus and duodenum (n = 17) and DA type III with a BBD (n = 3). These results support the role of fetal swallowing and fluid absorption by the fetal gastro-intestinal tract in the regulation of amniotic fluid volume.