Estimation of fetal weight by ultrasound prior to 33 weeks gestation

The aim of this study was to develop an accurate formula for the ultrasonic prediction of fetal weight for infants < 33 weeks gestational age and less than or equal to 1500 g birth-weight. The subjects comprised live births f ree of lethal malformations or chromosomal anomalies, < 33 weeks gestationa l age and with birthweights less than or equal to 1500 g born in the Royal Women's Hospital between January 1990 and March 1996. All subjects had accu rate gestational age confirmed by ultrasound prior to 20 weeks gestation an d ultrasound measurements within 72 hours of birth of biparietal diameter ( BPD), femur length (FL) and abdominal circumference (AC). A formula with th e highest explained variance was computed by linear regression analysis usi ng the three fetal variables in various combinations from 54 infants born b etween January 1990 and December 1993. The optimal formula was: Log(10)birthweight = 0.714627 + 0.077362.AC + 0.058758.BPD + 0.287037.FL - 0.011274.AC.FL The new formula was more accurate compared with existing formulae when test ed in a separate cohort of 39 infants born between January 1994 and March 1 996.