The Effect of Parental Weight and Genetics on the Body Mass Index of Very Low Birth Weight Infants as They Reach School Age.

Background: Prematurely born individuals are usually of low or normal weight in childhood; in adulthood, however, their probability of being overweight is twice that of persons born at full term. There is not yet any way to predict the weight development of premature babies.

Methods: A polygenic BMI score (BMI = body-mass index), calculated from the often very small individual effects of more than 2 million genetic variants, was recently described for adults. We studied the possible association of this score with the course of BMI in premature babies over time, from infancy up to the age of 10-14 years.

Results: 508 individuals were included in the study. At the age of 5-7 years, their mean body weight was 18.8 ± 3.3 kg. The difference between the highest and lowest deciles of the polygenic score was 3.3 kg. At age 10-14, the average body weight was 41.3 ± 11.3 kg, and the difference between the highest and lowest deciles had increased to 9.2 kg. In persons with birth weight under the 10th percentile (n = 68), the difference was 19.2 kg (30.9 kg vs. 50.1 kg). The polygenic BMI score was significantly associated with the BMI z-scores of the overall group and the subgroup of growth-retarded children.

Conclusion: Extreme values of a polygenic BMI score are strongly associated with the weight development of preterm infants as they develop into children aged 10-14. The large effect size implies that this score may aid in the counseling of prematurely born children and their parents.