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.