A novel approach to intertriplet birth weight discordance

Objective: This study was undertaken to evaluate intertriplet birth weight discordance. Study Design: Birth weight discordance greater than 25% was evaluated in a cohort of 2804 US live-born triplets. Symmetric and high- and low-skew sets were defined by the rank of the middle triplet between the heavier and the lighter triplets. Frequencies of discordance level and type were analyzed by gestational age, parity, and total triplet birth weight. Results: Discordance of 25.1% to 35% and greater than 35% was found in 19.4% and 9.5% of the triplets analyzed, respectively. Frequencies of greater than 25% discordant sets demonstrated polynomial relationship to gestational age (R2 = 0.94, P< .001) total triplet birth weight deciles (R2 = 0.97, P< .001). Frequencies of discordance type are unchanged throughout gestation. Conclusion: Birth weight discordance in triplets is frequent and large and implies exhaustion of fetal growth potential despite a uterine environment that appears to perform at maximal effort in these pregnancies. (Am J Obstet Gynecol 2003;188:1026-30.)