Mid-trimester diagnosis of bladder neck obstruction by ultrasound and paracentesis.

A bladder neck obstruction was suspected after ultrasound investigation at 16 weeks' gestation. Evaluation of protein content in the amniotic fluid, fetal ascites, and fluid from the overdistended bladder supported the diagnosis. Bladder outflow obstruction in the second trimester of pregnancy was not associated with raised alphafetoprotein levels in the amniotic fluid and maternal serum.