Growth of very low birth weight infants to age 20 years

Intrauterine and neonatal growth failure of very low birth weight (VLBW; <1500 g) infants may influence adult growth attainment and have long-term implications for adult health. As part of a longitudinal study of VLBW infants, we sought to examine gender-specific changes in growth from birth to 20 years old and to identify the correlates of growth attainment at 20 years old.

A cohort of 103 male and 92 female VLBW infants who had a mean birth weight of 1189 g and mean gestational age of 29.8 weeks, were born from 1977 through 1979 and treated at Rainbow Babies and Children's Hospital in Cleveland, Ohio, and were free of neurosensory impairment were followed prospectively from birth and compared with a population-based sample of 101 male and 107 female normal birth weight (NBW) controls selected at 8 years old. Maternal sociodemographic status and infant birth and neonatal data did not differ significantly between male and female VLBW subjects. However, male VLBW subjects had significantly higher rates of rehospitalization during infancy than female VLBW (39% vs 21%). At 20 years, their rates of chronic illness were similar (18% vs 24%).

Weight and height z scores were computed at birth, 40 weeks, 8 and 20 months, and 8 and 20 years among the VLBW subjects, and at 8 and 20 years among the NBW controls. Body mass index (BMI) z scores were computed at 8 and 20 years. Among the VLBW subjects, gender-specific longitudinal growth measures were examined at birth, at the expected term date (40 weeks corrected age), and at 8 and 20 months, and 8 and 20 years of age. In addition, we compared the weight, height, and BMI of the VLBW and NBW controls at 8 and 20 years. Predictors of 20-year growth were examined via multivariate analyses.

Among the VLBW males, mean weight for age z scores at birth, 40 weeks, and 8 years were -0.7, -1.8, and -0.5; and height for age z scores were -1.2, -2.6, and -0.5, respectively. For VLBW females, mean weight for age z scores were -1.1, -2.0, and -0.2 and height for age z scores were -1.2, -2.4, and -0.2, respectively. At 8 years of age, VLBW males had a significantly lower mean weight, height, and BMI than NBW controls, whereas VLBW females differed significantly from their NBW controls in mean weight and BMI but not in height. Catch-up growth in weight, height, and BMI occurred between 8 and 20 years among VLBW females but not among VLBW males who remained significantly smaller than their controls at 20 years old. At 20 years mean weight of VLBW males was 69 kg versus 80 kg for controls (z score -0.4 vs +0.5); mean height was 174 cm versus 177 cm (z score -0.4 vs +0.03) and mean BMI was 23 versus 26, respectively. For VLBW females, mean weight was 65 kg versus 68 kg for controls (z score +0.3 vs +0.5), mean height was 162 versus 163 cm (z score -0.3 vs -0.1) and mean BMI was 25 versus 25, respectively. Rates of obesity (BMI >30) for VLBW males were 7% compared with 15% for controls and for VLBW females 15% compared with 18% for controls. Age of menarche was 12.4 years for VLBW females and 12.3 years for controls. Nineteen (18%) male and 20 (22%) female VLBW subjects were born small for gestational age (SGA; weight less than -2 standard deviation for gestational age). At 20 years, significantly more SGA than appropriate for gestational age VLBW males remained subnormal (less than -2 standard deviation) in weight (32% vs 6%) and height (21% vs 4%), whereas rates of subnormal growth did not differ significantly between SGA and appropriate for gestational age females (weight 5% vs 1%, height 0% vs 7%). Predictor variables included in the multivariate analyses of 20-year growth attainment were maternal education and height, race, birth weight z score (a measure of intrauterine growth failure), neonatal hospital stay (a measure of neonatal illness), and chronic illness at 20 years. Twenty-year weight was predicted by black race and chronic illness among females. Twenty-year height was predicted by maternal height and birth weight z score among both males and females and by duration of neonatal hospital stay among males only. In a separate model, when we examined the effect of being SGA at birth instead of the effect of birth weight z score, SGA birth was predictive of 20-year height among males but not among females.

VLBW females catch up in growth by 20 years of age whereas VLBW males remain significantly shorter and lighter than controls. Since catch-up growth may be associated with metabolic and cardiovascular risk later in life, these findings may have implications for the future adult health of VLBW survivors.