CLINICAL ARTICLE Longitudinal reference intervals for Doppler velocimetric parameters of the fetal renal artery correlated with amniotic fluid index among low-risk pregnancies Camilla O. Figueira, Fernanda G. Surita, Márcia S.J. Dertkigil, Simiran L. Pereira, João R. Bennini Jr, Sirlei S. Morais, José G. Cecatti ⁎ Department of Obstetrics and Gynecology, School of Medical Sciences, University of Campinas, Campinas, Brazil abstract article info Article history: Received 10 November 2014 Received in revised form 7 May 2015 Accepted 25 June 2015 Keywords: Amniotic fluid index Doppler velocimetry Fetal renal artery Longitudinal study Low-risk pregnancy Reference intervals 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 N 0.05 for all). The intraclass correlation co- efficients for intra-observer and inter-observer variability indicated good reproducibility of SV, but the reproduc- ibility 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. © 2015 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved. 1. Introduction The advent of fetal hemodynamic studies performed in conjunction with Doppler velocimetry of the umbilical arteries enabled clinicians to detect abnormal fetal blood flow [1] and evaluate perfusion of the fetal or- gans [2]. Technological advances have permitted the study of other ves- sels, including the renal artery, thereby improving fetal surveillance [1,3]. The renal artery emerges straight from the aorta. Renal size, blood flow, and peak systolic velocity (SV) rise during gestation [4,5], whereas the PI decreases owing to increased perfusion of the kidneys [6,7]. Studies have assessed Doppler velocimetric parameters in an attempt to correlate these measures with several clinical situations, such as fetal growth re- striction and hypertensive disorders of pregnancy, and with the amount of amniotic fluid (the amniotic fluid index; AFI) [3,8–10]. Amniotic fluid is a well established parameter of fetal well-being [11]. During the second half of pregnancy, amniotic fluid is predominantly composed of fetal urine, which supports the hypothesis that oligohydramnios could be re- lated to renal volume and function [12]. However, the association between fetal renal artery Doppler velocimetric parameters and AFI re- mains controversial. Although fetal hemodynamic studies were first conducted in the mid- 1970s [1], many benefits of Doppler evaluation for fetal surveillance have already been proven. Because some parameters are incompletely under- stood, new studies could suggest valuable improvements for clinical ob- stetric practice. Such studies might include an integrated evaluation of the fetal renal artery and umbilical artery, and their relationship with AFI, because early changes in Doppler velocimetric parameters of renal ar- tery starting in the second trimester could indicate an early stage of fetal renal impairment and enable close follow-up of affected pregnancies. Understanding the evolution of the Doppler velocimetric parameters in uncomplicated and complicated pregnancies is important for correlating data obtained in pregnancies characterized by fetal impairment. The aims of the present study were to establish standard reference intervals of PI and SV for the fetal renal artery; to evaluate the reproduc- ibility of the method; and to correlate the Doppler velocimetric param- eters with AFI among women with low-risk pregnancies. 2. Material and methods A longitudinal prospective study was conducted among a cohort of women with low-risk pregnancies who attended outpatient clinics at the University of Campinas Medical School, Campinas, Brazil, between International Journal of Gynecology and Obstetrics xxx (2015) xxx–xxx ⁎ Corresponding author at: Department of Obstetrics and Gynecology, School of Medical Sciences, University of Campinas, Rua Alexander Fleming 101, PO Box 6030, 13083–881 Campinas, São Paulo, Brazil. Tel.: +55 19 3521 9482; fax: +55 19 3521 9304. E-mail address: cecatti@unicamp.br (J.G. Cecatti). IJG-08405; No of Pages 4 http://dx.doi.org/10.1016/j.ijgo.2015.05.010 0020-7292/© 2015 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved. Contents lists available at ScienceDirect International Journal of Gynecology and Obstetrics journal homepage: www.elsevier.com/locate/ijgo Please cite this article as: Figueira CO, et al, Longitudinal reference intervals for Doppler velocimetric parameters of the fetal renal artery correlated with amniotic fluid inde..., Int J Gynecol Obstet (2015), http://dx.doi.org/10.1016/j.ijgo.2015.05.010