Is oligohydramnios in postterm pregnancy associated with redistribution of fetal blood flow?

Our purpose was to determine whether postterm patients with oligohydramnios differ in their fetal and umbilical blood flow distribution from those with a normal volume of amniotic fluid.

Pulsed-wave Doppler imaging was used prospectively to determine the resistance index in the fetal middle cerebral, renal, and umbilical arteries in 57 postterm (i.e., > 41 weeks' gestation) pregnancies. Semiquantitative assessment of amniotic fluid volume was obtained by use of the ultrasonographically determined amniotic fluid index.

Oligohydramnios (amniotic fluid index < 5 cm) was detected in 15 patients; 42 patients with a normal amniotic fluid index served as a control group. The various resistance index values and the ratio s among them were not significantly different when patients with oligohydramnios were compared with controls (0.51 +/- 0.1 vs 0.52 +/- 0.06, 0.63 +/- 0.1 vs 0.64 +/- 0.08, and 0.71 +/- 0.08 vs 0.73 +/- 0.05 for the umbilical, middle cerebral, and renal arteries, respectively). However, the mean birth weight (in grams) was significantly lower (3297 +/- 438 vs 3742 +/- 448, p < 0.003), in the oligohydramnios group.

Oligohydramnios was not associated with a major redistribution of blood flow in postterm patients, suggesting that the cause of oligohydramnios in these patients is related to birth weight rather than to renal perfusion.