Infant weight gain patterns and childhood BMI: Twin vs. singleton comparison

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Created On: 16/10/2025

This study aimed to explore how various aspects of infant weight development are linked to body mass index (BMI) during childhood, comparing patterns observed in twins to those in singletons.

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Key take away

Early weight gain during infancy is linked with childhood BMI in singletons, but not in twins.

Background

This study aimed to explore how various aspects of infant weight development are linked to body mass index (BMI) during childhood, comparing patterns observed in twins to those in singletons.

Method

Data were sourced from the PROMISE study, a large-scale, electronic health record-based cohort that included pregnant women and their children born between 2004 and 2020 across multiple community healthcare settings in the U.S. The analysis included 227 male and 250 female twins, compared against 13,952 male and 13,500 female singletons.

Secondary analyses used matched groups of 2,270 male and 2,500 female singletons, aligned by gestational age and sex. Infant weight patterns from birth to 24 months were modeled via the Jenss growth curve. Linear regression analyses were executed to examine the connection between specific weight trajectory characteristics and BMI z-scores (BMIz) measured at ages 3 and 5 years, separately for each group.

Result

For twins, an increase in weight during late infancy (approximately 12 to 24 months) was the only factor markedly linked to higher BMIz at both 3 and 5 years of age, with this trend being more pronounced in female twins than in males. Conversely, in the singleton cohort, BMIz at 3 and 5 years was linked not only with late infancy weight gain but also with weight at birth, early infancy gain (0–6 months), and mid-infancy gain (6–12 months). The pattern in the gestational age-matched singleton group closely mirrored that of the broader singleton population.

Conclusion

Unlike singletons—where weight gains across all infancy stages were associated with later BMI—twins showed a distinct pattern, with only weight gain in late infancy contributing to BMI in early childhood. These results highlight fundamental differences in the growth-BMI relationship between twins and singletons, pointing towards potentially divergent underlying mechanisms.