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

OBJECTIVE: Our purpose was to determine whether postterm patients with oligohydramnios differ in their fetal and umbilical flow distributions from those with a normal volume of amniotic fluid. STUDY DESIGN: 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 weeksʹ gestation) pregnancies. Semiquantitative assessment of amniotic fluid volume was obtained by use of the ultrasonographically determined amniotic fluid index. RESULTS: 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 ratios 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. CONCLUSION: 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.