Early Infancy Weight Gain Patterns Are Associated with Child Body Mass Index in Singletons but Not Twins

To assess the relationship between characteristics of infant weight trajectory and child body mass index (BMI) in twins compared with singletons.

Data were extracted from the PROMISE study, an electronic health record-based cohort of pregnant individuals and their children born from 2004 to 2020 across community-based health care organizations in the United States. We compared 227 and 250 male and female twins with 13 952 and 13 500 male and female singletons, respectively, and secondary comparison groups of 2270 male and 2500 female singletons matched to twins on gestational age and sex. Infant weight trajectory (0-24 months) was modeled with the Jenss model. Linear regression was used to determine associations between weight trajectory characteristics and BMI z-score (BMIz) at 3 and 5 years within each group.

Among twins, only late infancy weight gain (∼12-24 months) was positively associated with BMIz at 3 and 5 years, with a stronger association among female compared with male twins. In contrast, among singletons, starting weight, early infancy weight gain (∼0-6 months), mid-infancy weight gain (∼6-12 months), and late infancy weight gain (∼12-24 months) were associated with BMIz at 3 and 5 years. Associations among GA-matched singletons were similar to the full singleton group.

Among twins, early and mid-infancy weight gains were not associated with child BMIz, with only late infancy weight gain showing an association. In contrast, among singletons, all parameters of infant weight trajectory were associated with child BMIz. These findings suggest different drivers of infant weight gain and childhood BMI in twins and singletons.