(812) Triplet-specific birthweight reference and its utility in predicting neonatal outcomes: a retrospective cohort study

Objective:
We tried to develop a triplet-specific birthweight reference and evaluate its predictive accuracy for adverse neonatal outcomes compared with singleton and twin references.

Study Design:
This retrospective cohort included 491 triplet trios delivered at a tertiary center (Nov 1997–Feb 2024). Birthweights of trichorionic and dichorionic triplets were used to construct gestational age–specific percentiles (3rd–97th) via the lambda-mu-sigma method. Small-for-gestational-age (SGA) was defined < 10th percentile using singleton, twin, or triplet references. Unlike most growth references based on ultrasonographic estimated fetal weight (EFW), we used actual birthweight because EFW is less reliable in triplet pregnancies than in singleton and twin pregnancies due to technical limitations and labeling errors. Composite adverse neonatal outcome (neonatal death, respiratory distress syndrome, bronchopulmonary dysplasia, persistent ductus arteriosus, pulmonary hypertension, intraventricular hemorrhage, periventricular leukomalacia, retinopathy of prematurity, necrotizing enterocolitis, or early-onset sepsis) was compared across references.

Results:
Monochorionic triplets had lower birthweights than di- or trichorionic triplets (p=.004). No significant birthweight difference was observed between male and female triplets (p=.782). Triplet growth diverged from twins and singletons after 28 weeks. Using singleton, twin, and triplet references, 40.5%, 22.2%, and 8.3% of neonates were SGA, respectively. Neonates classified as SGA by singleton or twin reference, but non-SGA by triplet reference had no increased risk of adverse outcomes compared with non-SGA (singleton aOR 1.25, 95% CI 0.86–1.82; twin aOR 0.81, 95% CI 0.51–1.27). But, SGA by triplet reference showed significantly increased risk for adverse neonatal outcome (aOR 2.15, 95% CI 1.43-3.24).

Conclusion:
The triplet-specific birthweight reference reduces overdiagnosis of small but healthy neonates and more accurately identifies those at genuine risk for adverse outcomes, supporting its clinical utility in guiding optimal management of triplet pregnancies.