INTRAPARTUM ASSESSMENT BY HOUSE STAFF OF BIRTH-WEIGHT AMONG TWINS

Objective: To determine among twins in labor: 1) the relative accuracy of an intrapartum sonographic estimate of the birth weight for both f etuses using biparietal diameter and abdominal circumference, 2) the a ccuracy of detecting discordant growth (difference in actual birth wei ghts greater than or equal to 15%), and 3) the estimate of fetal weigh t for nonvertex twin B that would reliably avoid breech extraction of infants less than 1500 g. Methods: Retrospectively, we identified and analyzed parturients with twins who had an intrapartum sonogram perfor med by a house officer assigned to the labor and delivery suite. Resul ts: The mean birth weight (+/- standard deviation) for the twin A grou p was 1910 +/- 628 g and for twin B was 1869 +/- 668 g. The mean stand ardized absolute errors for the twin A group (121 +/- 118 g/kg) and th e twin B group (92 +/- 67 g/kg) were not significantly different (P = .06). Analysis of variance revealed that regardless of the presentatio n of the fetuses, the mean standardized absolute error was not signifi cantly different (P = .10). Using a difference in the estimates of bir th weight of 15% or greater, the positive and negative predictive valu es of detecting discordant growth within a twin pair were 53 and 83%, respectively. Among 30 vertex-nonvertex twin pairs, 12 of the second f etuses had actual birth weights of 1500 g or less, and all were estima ted to weigh less than 1700 g. Conclusions: The intrapartum sonographi c estimate of fetal weight in twin pregnancy by house staff appears re liable, and the accuracy of prediction is similar regardless of presen tation, discordance, or actual birth weight greater or less than 1500 g. To avoid vaginal delivery of a persistent nonvertex twin B with a b irth weight of 1500 g or less, a sonographic estimate of 1700 g for th e second fetus may be adequate.