Relationship Between Amniotic Fluid Index and Ultrasound Estimated Fetal Weight in Healthy Pregnant African Women

INTRODUCTION: Fetal weight (FW) estimation in late pregnancy is an important guide in obstetric care. Amniotic fluid protects the fetus against traumatic and infective insults. There possibly exists a relationship between FW and amniotic fluid index (AFI) that can be estimated by ultrasonography. MATERIALS AND METHODS: Two hundred and fifty-eight low-risk pregnancies were prospectively studied by means of ultrasound over a 12-month period. FW was estimated using a combination of fetal parameters; bi-parietal diameter, fetal trunk cross sectional area, and femur length. AFI was assessed using the 4-quadrant method. Spearman's correlation was used to test possible relationship between amniotic fluid indices and estimated FW pairs. The level of statistical significance was set at P ≤ 0.05. RESULTS: The mean AF1 and estimated fetal weight (EFW) pairs were as follows: at 27-29 weeks the values were 172.1 mm and 1,250.2 g; at 30-32 weeks AF1 and EFW values were 170.3 mm and 1,648.0 g; at 33-35 weeks values were 162.3 mm and 2,273.5 g; at 36-38 weeks values were 144.09 mm and 2,906.1 g; at 39-40 weeks AF1 and EFW values were 125.0 mm and 3,222.6 g. Overall, there was no statistically significant relationship between AFI and EFW (P > 0.05; r = 0.241). CONCLUSION: While FW calculations and amniotic index showed variations in value in late pregnancy, there does not appear to be a linear relationship between ultrasound estimate of FW and amniotic index. The implication of this is that fetal size need not be taken into cognizance when alterations in amniotic fluid values are noted.