Serial third trimester ultrasound examinations in predicting fetal weight

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.