Doppler Study of the Fetal Renal Artery in Oligohydramnios with Post-term Pregnancy

ObjectiveThe aim of the study was to investigate the fetal renal artery impedance and hemodynamics in the context of post-term pregnancy with oligohydramnios, using Doppler indices.MethodsThis is a prospective study which took place between December 2011 and March 2013. Fetal renal artery Doppler was performed in women at gestational age between 40.1 weeks and 41.3 weeks with singleton pregnancies. The fetal renal artery Doppler resistance index (RI), pulsatility index (PI), systolic/diastolic ratio (S/D), acceleration time (AT), blood flow (BF), fetal renal volume, APGAR, and cesarean ratio 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 < 5 cm).ResultsWe studied 84 well-dated, singleton, post-term pregnancies, referenced from the high post-term pregnancy obstetric service. Forty-one patients (48.1%) had oligohydramnios. Patients with oligohydramnios had higher S/D, RI, and AT. The fetal renal artery BF (FRABF) was lower in patients with oligohydramnios than those without oligohydramnios (p = 0.037). Stepwise logistic regression using renal artery Doppler indices found FRABF to be the only significant predictor of oligohydramnios: p = 0.012, p < 0.005 [odds ratio = 0.821, 95% confidence interval (CI) = 0.769–0.912].ConclusionIn oligohydramnios in the context of post-term pregnancies, there is an increased resistance in the fetal renal vascular bed. The reduced FRABF suggests that increased arterial impedance is an important factor in the development of oligohydramnios. This study supports the idea of increased vascular resistance in the fetal renal bed in patients in post-term pregnancies. We think that fetal renal artery Doppler measurement should be part of a routine daily clinical obstetric practice in post-term pregnancies with oligohydramnios.