Comparing child growth between small-for-gestational age twins and singletons in the upstate KIDS cohort

Twins have an increased risk of being small-for-gestational-age (SGA) at birth compared to singletons, but little is known about their growth in childhood. It’s hypothesized that the maternal-fetal unit may become less capable of sustaining optimal growth in twin fetuses starting around 32 weeks indicating that some smaller birth size may be due to adaptation. Whether SGA twins show the same postnatal growth patterns as singletons born SGA, who may be growth-restricted, is unknown. Upstate KIDS collected longitudinal data on child growth among twins and singletons. We used linear mixed models to compare z scores for height, weight, and BMI at 0-3 and 7-9 years of age among appropriate-for-gestational age (AGA) twins and singletons, SGA singletons, and two groups of SGA twins (Figure): uncertain SGA twins (< 10th percentile for birthweight by a singleton reference but >10th% by a twin reference) and true SGA twins (< 10th% by a twin reference). SGA complicated 9% of singleton and 29% of twin births using a singleton reference. Compared to SGA singletons, true SGA twins were shorter (β= -0.93; CI -1.06, -0.81) and weighed less (β= -0.74; CI -0.83, -0.66) at 0-3 years, while uncertain SGA twins were similar in size (Table). Beta (β) indicates the mean difference in z scores between SGA singletons and twin groups. By 7-9 years, true SGA twins were similar in size to SGA singletons; uncertain SGA twins tended to be larger than SGA singletons in weight (β=0.30; CI -0.04, 0.65) and height (β=0.25; CI -0.17, 0.67), though differences were not significant. Though a high percentage of twins were classified as SGA, their growth patterns did not follow those of singletons who are born SGA. True SGA twins were slightly smaller than SGA singletons in toddlerhood, but similar in size by 7-9 years. In contrast, twins classified by a singleton birthweight reference and not a twin reference may be larger than SGA singletons at 7-9 years, indicating a different phenotype of SGA for twins consistent with in utero physiologic adaptation.View Large Image Figure ViewerDownload Hi-res image Download (PPT)