Estimation of Fetal Body Weight in Twins: A New Mathematical Model


Objectives: Evaluation of a new mathematical formula (FEMUR 4) derived from twin population to estimate fetal weight in twins using ultrasound.Design: retrospective analysis of ultrasonic measurements of 103 twins from 30 – 40 wks of gestation born within 3 days of ultrasonic examination.Setting: Al Yarmouk Teaching Hospital, Baghdad, Iraq.Methods: Between Sep. 2004 and Dec. 2005 at the Obstetric and Gynecological department in Al- Yarmouk Teaching Hospital a cross-sectional ultrasonic measures obtained from 107 twin pregnancies, estimated fetal weight was calculated using mathematical model of Campbell, Shepard, and Hadlock, the calculations were repeated for the model Femur 4, all models were compared against Femur 4.Results: Femur 4 had been found to have positive correlation with actual birth weight with coefficient of determination of linear regression value of 0.859. It had the percent of estimation of fetuses within 10 percent of their actual BW (87.9 percent). It had the mean percentage error of 0.03 (6.52) compared to singleton derived formulae. In fetal growth deviation it had been found to have accuracy rate in detecting those below their 10th centile for gestational age of (90.8 percent) and (96.1 percent) in disclosing those who were growth discordant twins.Conclusion: Femur 4 seems to be more reliable than singletone derived formulae in estimating fetal weight in twins, and in general, American population designed formulae are probably still applicable on our Iraqi people.Key Words: twin pregnancy• new formula• estimated body weight• ultrasound