The association of fetal growth rate and growth in first year of life with childhood overweight: a cohort study.

Background: There is an increasing focus on the first 1000 days from conception to two years of age as a period of importance for future weight. We aimed to describe the interaction between fetal and infant growth and their association with and ability to predict childhood overweight.

Methods: We used routinely collected fetal growth data from Aarhus University Hospital and child growth data from Aarhus Municipality, 2008-2018. The outcome was overweight at age 5-9 years. The fetal growth rates at weeks 28 and 34 were extracted from individual trajectories using mixed models. We identified patterns of infant BMI Z-score growth using latent class analysis and estimated odds ratios of overweight at age 5-9 years dependent on fetal and infant growth. Predictive capabilities were assessed by comparing areas under the ROC-curves (AUCROC) of the prediction models.

Results: In 6206 children, we identified three infancy growth patterns: average, accelerated, and decelerated growth. We found 1.09 (95% CI: 1.06-1.12) greater odds of being overweight for every 10 g/week increase in fetal growth rate at week 34. Compared with average growth, accelerated infant growth was associated with 1.52 (95% CI: 1.20-1.90) greater odds of overweight. Combining fetal and infant growth, children with average fetal growth and accelerated infant growth had 1.96 (95% CI: 1.41-2.73) greater odds of overweight. Fast fetal growth with decelerated infant growth was not associated with being overweight (OR: 0.79 (95% CI: 0.63-0.98)), showing that infant growth modified the association between fetal growth and overweight. When fetal growth was added to a prediction model containing known risk factors, the AUCROC remained unchanged but infant growth improved the predictive capability (AUCROC difference: 0.04 (95% CI: 0.03-0.06)).

Conclusion: Fetal and infant growth were independently associated with overweight, but distinct combinations of fetal and infant growth showed marked differences in risk. Infant, but not fetal, growth improved a prediction model containing known confounders.