THE INTRAUTERINE PONDERAL INDEX IN RELATION TO BIRTH-WEIGHT DISCORDANCE IN TWIN GESTATIONS

Objective: To establish the relationship between the fetal ponderal in dex and birth weight discordance in twins. Method: The fetal ponderal index (estimated fetal weight divided by femur length(3)) was calculat ed in 86 pairs of twins delivered within 2 weeks of the last sonograph y and analyzed in relation to birth weight discordance. Results: A wea k but significant correlation between fetal ponderal index and birth w eight (r = 0.26, P < 0.0007) but no correlation with gestational age ( r = 0.035, P = 0.65) were found. Members of concordant pairs (< 15% bi rth weight difference) had a significantly higher fetal ponderal index compared with members of mildly (15-25%) discordant pairs (P < 0.02), but not as compared with members of severely discordant (>25%) pairs. Conclusion: The characteristics of the fetal ponderal index in twins are similar to those in singletons. Fetal size seems to be diminished in severe but not in mild discordants. However, in its present form, t he fetal ponderal index is a poor predictor of discordant growth and t herefore should be employed cautiously in twin gestations.