Renal artery Doppler investigation of the etiology of oligohydramnios in postterm pregnancy.

OBJECTIVE

To investigate the etiology of oligohydramnios in postterm pregnancy using Doppler velocimetry.

METHODS

Renal and umbilical artery Doppler velocimetry were performed in women with singleton postterm (287 days' or more gestation) pregnancies. The renal and umbilical artery Doppler resistance index (RI) and end-diastolic velocity were measured. Stepwise logistic regression and the two-tailed t test were used to determine whether the Doppler indices correlated with oligohydramnios (amniotic fluid index less than 5 cm).

RESULTS

We studied 147 well-dated, singleton, postterm pregnancies, of which 21 (14.3%) had oligohydramnios. For the study cohort, the mean (+/-standard deviation) gestational age at Doppler was 41.4 +/- 0.45 weeks and at delivery 41.8 +/- 0.47 weeks. Stepwise logistic regression using renal and umbilical artery Doppler indices found the renal RI to be the only significant predictor of oligohydramnios: beta = -10.4186, P <.05 (odds ratio [95% confidence interval (CI)] = 0, 0.88). The renal artery RI was significantly higher in cases with oligohydramnios (RI: mean (+/-standard error) = 0.8843 +/- 0.11 versus 0.8601 +/- 0.05, P <or= 0.05). A renal artery Doppler end-diastolic velocity below the mean for gestation significantly increased the risk of oligohydramnios: relative risk (95% CI), 1.5 (1.1, 2.0).

CONCLUSION

Renal artery Doppler was more predictive of oligohydramnios than the umbilical RI. The reduced renal artery end-diastolic velocity suggests that increased arterial impedance is an important factor in the development of oligohydramnios in prolonged pregnancies.