Objective: The aim of this study was to compare the accuracy of estimated fetal weights obtained by ultrasonographies performed at different weeks in the third trimester and just before delivery.
Methods: A total of 664 patients underwent three serial ultrasonographic examinations in the third trimester. The sonographically estimated fetal weight was calculated using the Hadlock formula and then converted into percentiles. The estimated fetal weight percentiles were compared with the actual birth weight percentiles at delivery.
Results: Mean maternal age was 30±4 years (18-42 years), mean gestational age at first ultrasound was 32±0.5 weeks (30.4-33.6 weeks), mean gestational age at second ultrasound was 36±0.4 weeks (35-36.9 weeks), mean gestational age at third ultrasound was 38.6±1 weeks (36.3– 42 weeks). Mean gestational age at delivery was 39± 1 weeks (36-42 weeks), mean birth weight was 3422±423 grams (1900-4900 grams). Correlation coefficients of estimated fetal weights percentiles at first, second and third ultrasounds were significantly correlated with birth weight percentiles (r=0.556, p<0.001), (r=0.623, p<0.001), (r=0.747, p<0.001, respectively).
Conclusion: Ultrasonographic fetal weight estimations correlate with the actual birth weight better when performed in the late third trimester, but ultrasonographic fetal weight estimation early in the third trimester may allow for better follow up and planning of delivery both in small and large for gestational age fetuses.