Objective: 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.
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 weeks' 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 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.
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.