Longitudinal reference intervals for Doppler velocimetric parameters of the fetal renal artery correlated with amniotic fluid index among low-risk pregnancies.

OBJECTIVE: To establish longitudinal reference intervals for pulsatility index (PI) and systolic velocity (SV) of the fetal renal artery, and to evaluate their correlation with the amniotic fluid index (AFI).

METHODS: A prospective longitudinal study was conducted among women with low-risk pregnancies who attended outpatient clinics at the University of Campinas Medical School, Brazil, at 16-19 weeks of pregnancy between April 1, 2008, and March 31, 2010. Doppler velocimetric measurements of the fetal renal artery and assessments of the AFI were undertaken at 4-week intervals to 36 weeks, and every 2 weeks thereafter until delivery.

RESULTS: A total of 63 women were enrolled. The PI of the fetal renal artery showed little variation during pregnancy, whereas SV values increased to 36-37 weeks of pregnancy and decreased thereafter. No correlations were found between the AFI and the fetal renal artery Doppler velocimetric parameters (P>0.05 for all). The intraclass correlation coefficients for intra-observer and inter-observer variability indicated good reproducibility of SV, but the reproducibility of PI was lower.

CONCLUSIONS: The AFI did not correlate with fetal renal artery Doppler velocimetric measures among low-risk pregnancies. However, investigations are needed among high-risk pregnancies.