Birth weight discordance and adverse fetal and neonatal outcomes among triplets in the United States

OBJECTIVE: To examine the association between intratriplet birth weight discordance, fetal and neonatal mortality, and smallness for gestational age. METHODS: The 1995-1997 Centers for Disease Control and Prevention's Matched Multiple Birth file was used for this analysis. Birth weight discordance was calculated as the difference in birth weight between the largest and the smallest triplet's weight and expressed as percentage of the largest triplet's weight. For the middle-weight triplet, we also used the largest triplet's weight as a reference in calculating percentage birth weight discordance, which was then grouped into quintiles. RESULTS: Among 15,511 triplet live births and fetal deaths (at least 20 weeks' gestation), 35% had less than 10% birth weight discordance, 19.3% had 10-15%,16.4% had 15-21%, 15.2% had 21-29%, and 14.1% had 29% or more. After controlling for confounders, the risk of fetal death associated with quintile V was significantly higher than that associated with quintile I for smallest (odds ratio [OR] 10.88; 95% confidence interval [CI] 4.87, 26.56), middle (OR 22.6; 95% CI 11.05, 46.3), and largest (OR 2.41; 95% CI 1.01, 5.89) triplets. Smallest and middle triplets in quintile V were more likely than quintile I triplets to be born small for gestational age (OR 26.0; 95% CI 17.1, 39.9 for smallest, and OR 13.4; 95% CI 8.01, 22.3 for middle). Birth weight discordance quintile was not associated with smallness for geatational age among largest triplets nor consistently with neonatal mortality among smallest, middle, or largest triplets. CONCLUSION: Increasing birth weight discordance was associated with increased risk of fetal death and smallness for gestational age. A birth weight discordance threshold of at least 29% should alert obstetricians for appropriate decision making. (Obstet Gynecol 2003;101:909-14. (C) 2003 by The American College of Obstetricians and Gynecologists).