A comparison of two different ultrasound methods for estimating fetal weight in preterm gestations

A prospective study was conducted to evaluate the estimation of fetal weight in preterm pregnancies by use of ultrasound measurements. Two equations for estimating fetal weight, one proposed by Shepard and associates and the other by Hadlock and associates, were evaluated. The ability to estimate fetal weight accurately was evaluated with respect to birth weight and menstrual age. Shepard's equation is associated with a lower mean signed percent error than Hadlock's, when the birth weight is less than 1500 g (4% vs 12%) or when the menstrual age is between 23 weeks to 30 weeks (2% vs 10%). However when the birth weight is between 1500 g and 3500 g, or the menstrual age is between 31 weeks to 36 weeks, Hadlock's equation has a lower mean signed percent error: 1% vs -4% for the birth weight category and 2% vs -3% for the menstrual age category. In preterm gestations both equations estimate fetal age weight with a low mean signed percent error--Shephard's -0.4% versus Hadlock's 6.0%.