The relationship between neonatal developmental status and post-natal nutritional status in Hungarian children

Does Fetal Growth Restriction Cause Later Obesity? Pitfalls in Analyzing Causal Mediators as Confounders

Recent studies finding that small-for-gestational-age (SGA) birth is associated with increased adiposity in childhood and adulthood have been based on analyses "adjusting" for height, weight, or body mass index (BMI; weight (kg)/height (m)2) measured concurrently with the adiposity measurement. To assess the potential for bias due to overadjustment for a causal mediator, we compared 2 approaches to analyzing the association between SGA birth and adiposity outcomes (skinfold thicknesses and bioelectrical impedance measurement of body fat) at age 11.5 years using the same data set in a cohort of Belarusian children followed from birth in 1996-1997 to age 11.5 years in 2008-2010. We 1) studied the association of SGA birth with adiposity, adjusting for baseline covariates only, and 2) made additional regression adjustment for concurrent height, weight, or BMI. The first approach yielded negative associations between SGA birth and all adiposity outcomes. Additional adjustment for concurrent weight or BMI reversed (i.e., to positive) the SGA-adiposity association. To explore the latter anthropometric measures as causal mediators, we also used marginal structural models to estimate the controlled direct effect of SGA birth. That effect was similar to the effect seen with the first approach when modeled on height, was null when modeled on BMI, but was confounded by differences in lean mass versus fat mass when modeled on weight.

Is restricted fetal growth associated with later adiposity? Observational analysis of a randomized trial

BACKGROUND

Several recent "developmental origins" studies have reported increased long-term risks of adiposity, especially truncal adiposity, among children born small for gestational age (SGA).

OBJECTIVE

We assessed the effects of SGA birth and weight gain in early infancy on adiposity at age 11.5 y.

DESIGN

From a cluster-randomized breastfeeding promotion trial in 17,046 Belarusian children, we measured height, weight, waist and hip circumferences, triceps and subscapular skinfold thicknesses, and bioimpedance measures of percentage body fat at age 11.5 y. Children born SGA (birth weight <10th percentile) and those born large for gestational age (LGA; >90th percentile for gestational age) were compared with those born appropriate for gestational age (AGA). Weight gain from birth to 6 mo was categorized as high (>0.67-SD increase in weight-for-age), low (>0.67-SD decrease in weight-for-age), or normal. Multilevel statistical models accounted for clustered measurement and controlled for maternal and paternal height and body mass index (BMI), maternal education, geographic region, urban compared with rural residence, and the child's exact age at follow-up.

RESULTS

Children born SGA had a significantly lower BMI, percentage body fat, and fat mass index than did those born AGA, with a dose-response effect across 2 subcategories of SGA (P < 0.001 for all comparisons). No difference was observed in waist-to-hip ratio, although the subscapular-to-triceps skinfold ratio was slightly but significantly (P < 0.001) higher in children born SGA. Differences among the study groups continued to increase since the previous follow-up at 6.5 y. SGA infants with catch-up growth in the first 3-6 mo had growth and adiposity measures intermediate between those born SGA without catch-up and those born AGA. Opposite effects of similar magnitude were observed in children born LGA.

CONCLUSION

The 11.5-y-old Belarusian children born SGA were shorter, were thinner, and had less body fat than their non-SGA peers, irrespective of postnatal weight gain. The Promotion of Breastfeeding Intervention Trial was registered at www.isrctn.org as ISRCTN-37687716.