Relationship of amniotic fluid index (AFI) in third trimester with fetal weight and gender in a southeast Nigerian population

BACKGROUND Amniotic fluid (AF) is one of the major determinants of fetal biophysical profile and can predict pregnancy outcome. Abnormal value of amniotic fluid index (AFI) may indicate fetal and maternal disorders. PURPOSE To establish reference standards for AFI for this population after 28 weeks of pregnancy and evaluate the relationship between AFI, the estimated fetal weight (EFWT), and fetal gender. MATERIAL AND METHODS A prospective cross-sectional estimation of AFI and FWT was done in 385 apparently healthy pregnant women in the gestational age range of 28-42 weeks. General scanning in longitudinal, transverse, and oblique directions of the abdomen was done to assess the fetal wellbeing and determine the fetal gender for each participant. AF was measured in each of the quadrants of the abdomen. The four values of the AF were summed to get the AFI. Measurement of the head circumference, biparietal diameter, abdominal circumference, and femoral length of the fetus were obtained. The EFWT was calculated using Hadlock's formula. The data were divided into five groups: 28-30 weeks 6 days; 31-33 weeks 6 days; 34-36 weeks 6 days; 37-39 weeks 6 days; and 40-42 weeks. AFI for the different gestational age group studied and their percentiles were obtained. RESULTS AFI normogram for the local population was established. Positive and significant correlations of AF and EFWT were seen in all the gestational age groups of the women. No significant correlations between AF and EFWT was seen in male fetuses. Regression equations of EFWT and AFI were obtained for female fetuses. CONCLUSION The normal range for AFI values for the third trimester was established and could be used to evaluate AFI in the studied population. Established fetal weight should be taken into account when interpreting AFI for female fetuses but this need not be applied for male fetuses.