Size at birth and gestational age as predictors of adult height and weight.

BACKGROUND Both birth length and birth weight are associated with height in adulthood and may have independent contributions to adult body size, but the effects of gestational age on these associations have not been fully evaluated. Our objective was to examine the independent contributions of gestational age, and of length and weight at birth, on adult (age 18 years) height and weight, with a special focus on the effects of being born preterm. METHODS In this nationwide cohort study, records of 348,706 male infants included in the Medical Birth Registry of Norway (1967-1979) were linked to the Norwegian Conscripts Service (1984-1999). Complete follow-up information, including deaths, emigration, and disability pension, was obtained for 94%. We analyzed length and weight at birth using standardized (z-scores) values and stratified by gestational age. RESULTS The positive association between birth length and adult height was stronger than between birth weight and adult weight (R = 7-9% compared with <0.1%, respectively). The strongest associations were seen among those born at gestational age 39 to 41 weeks. The effects of birth length on adult height, and of birth weight on adult weight, were considerably less among preterm births than among term births. Length and weight at birth each contributed independently to adult stature and body weight. The increase in adult weight per relative birth weight category was greatest for infants who were both heavy and long at birth. CONCLUSIONS Birth length is perhaps a better predictor of adult height and weight than birth weight, and should be considered as a possible risk factor for adult morbidity and mortality.