Perinatal & Pediatric
Twin-singleton infant growth differences exist independent of gestational age at birth Anna Booman* Anna Booman Alex Foster Miguel Marino Teresa Schmidt Jonathan M. Snowden Janne Boone-Heinonen
Background: Infant weight trajectory is routinely screened in clinical settings, with infants compared to a normative reference and interventions recommended. A common reference uses data from a population of singletons. Twins typically have lighter birth weight than singletons, in part due to earlier gestational age at birth (GA), so comparing them to this external reference may result in recommendations to increase feedings, with unknown appropriateness. Here, we compare growth trajectories of twins versus singletons, independent of GA, to inform twin-specific recommendations.
Methods: We used data from the PROMISE study, an electronic health record-based study derived from a network of community-based health care organizations. We included infants with a recorded GA and at least two weight measures before two years of age. We matched each of 320 twin males and 332 twin females to ten singletons on sex and GA (totaling 3,200 singleton males and 3,320 singleton females). Growth trajectories were fit using the Jenss mixed-effects model: parameters reflect (a) starting weight, (c) rate of growth in early infancy, (d) decreasing rate of growth in mid-infancy, and (b) rate of growth in late infancy.
Results: Twin males had the fastest weight gain in early infancy (c=1.70, 95% confidence interval [CI] 1.65, 1.75), catching up to and surpassing singleton males (c=1.59, 95% CI 1.58, 1.61) in weight by 8.5 months of life. Twin females had a similar rate of growth as singleton females throughout follow-up (e.g., c=1.52 for both), but given their lighter starting weight, caught up to, but did not surpass, singleton females by two years.
Discussion: Differences in growth between twins and singletons exist independent of GA and differ by infant sex. There may be unique factors related to twin gestation that affect infant growth beyond GA. Further research is needed to identify optimal growth and construct weight references for twins.
