Ultrasound prediction of fetal weight in prolonged pregnancy.

In this study we applied two commonly used birth weight prediction equations to a sample of 121 women with prolonged pregnancies. Subjects had sonographic measurements of biparietal diameter and abdominal perimeter taken within 2 days of delivery at Parkland Memorial Hospital. Although the two prediction equations were obtained from a population of women in New Haven, Connecticut, who delivered over a wide range of gestational ages, when the equations were applied to the sample of prolonged pregnancies in Dallas, Texas, there was a strong correlation (0.71) between predicted and actual birth weight. Moreover, reestimation of the New Haven equations with use of the Dallas data yielded similar regression coefficients. Finally, birth weight prediction equations for black, white, and Hispanic patients in Dallas were not significantly different. These findings suggest a remarkably constant relationship between fetal head and abdominal dimensions and birth weight over different gestational ages and for different population groups.