Comparison between singleton- and triplet-specific "growth" curves to detect growth restricted triplet infants

OBJECTIVE: To evaluate whether triplet- or singleton-specific growth standards should be used to define the growth restricted triplet fetus/neonate. STUDY DESIGN: We retrospectively compared the predictive values of singleton vs. triplet-specific "growth" standards using the neonatal ponderal index as reference for growth restriction. RESULTS: A ponderal index <1 SD from the mean was found in 356 (14.4%) of 2477 triplet infants. A total of 686 (27.7%) infants were small for gestational age (SGA) by singleton standards, but only 168 (6.8%) by triplet standards. After 31 weeks' gestation, triplet standards are significantly better associated with a low ponderal index (OR 2.0, 95% CI 1.1, 3.4 at 32 weeks to OR 4.1, 95% CI 2.8, 6.3 at 36-37 weeks), resulting in better positive predictive value and higher specificity of triplet standards in predicting a low ponderal index. CONCLUSION: Triplet birth weight standards are better than singleton standards at >31 but not at < or =31 weeks' gestation in predicting a low neonatal ponderal index.