Third Trimester Reference Values of Amniotic Fluid Index in a Group of Healthy Nigerian Women in Jos, Nigeria

Abstract

Objectives: To ascertain the normal values of amniotic fluid index in third trimester among Nigerian women with uncomplicated singleton pregnancies in Jos, Nigeria. Materials and Methods: This was a prospective cross-sectional study among 500 healthy pregnant women. Fifty women each were recruited at two-weekly interval from 28-36 weeks’ gestation and then weekly up to 41 weeks’ gestation. The uterine cavity was divided into four quadrants and using real-time ultrasonography, the vertical diameter of the largest pool of amniotic fluid was measured and summation of the values gave the amniotic fluid index (AFI). Mean, ranges, 5th, 10th, 50th, 90th and 95th percentiles for each gestational age were calculated using SPSS version 20 (IBM, Armonk, NY, USA). Results: Mean AFI among the entire study population was 18.1±3.1 cm (range of 10.4-26.8 cm) while the mean AFI for preterm and term pregnancies were 18.5±2.6 cm and 17.8±3.5 cm respectively. The AFI reference range for the study population was 13.6-24.6 cm. Amniotic fluid volume was highest at 28 weeks, stabilized and plateau between 37-39 weeks and declined after 40 weeks’ gestation. Using 5th and 95th percentile as lower and upper limits of normal, reference ranges for each gestational age was ascertained. Conclusion: Third trimester reference ranges of AFI is established and this can be used as a guide for evaluation of amniotic fluid volume in this obstetric population.