Fetal renal structure and the genesis of amniotic fluid disorders.

Newborn recipient twins in the transplacental transfusion syndrome have dilated renal tubules, enlarged bladders and an increased urinary output in the early neonatal period, suggesting that increased fetal micturition is responsible for hydramnios in the syndrome. There is the possibility that such micturition contributes to hydramnios in other disorders as well. In the present study, renal tubules were found to be dilated in single-born infants with a diverse group of disorders having hydramnios as a common feature. Many of the neonates had hypoplastic lungs, an abnormality whose role in the hydramnios is undetermined. Renal tubular lumina were of normal size in neonates associated with oligohydramnios due to chronic leak of amniotic fluid. Donor members of parabiotic transplacental transfusion pairs had contracted renal tubules which helps to explain their oligohydramnios.