Serum insulin-like growth factor 1 and serum growth-promoting activity during the first postnatal year in infants with intrauterine growth retardation

Follow-up from birth to age 12 months was obtained in 21 infants born with intrauterine growth retardation. Serum insulin-like growth factor 1 was measured by radioimmunoassay. The bioassayable growth-promoting activity of the serum was measured as the "thymidine activity" on lectin-activated lymphocytes at 5 days and 1, 3, 6, 9, and 12 months, and was compared with control values. Depending on their length at age 12 months, the intrauterine growth retardation infants were divided into three groups: at or above the average (n = 8, group A), between the mean and -2 SD (n = 7, group B), or less than -2 SD (n = 6, group C). No differences in nutritional indexes or in head circumference were found between the three groups. Insulin-like growth factor 1 was significantly lower at age 5 days in intrauterine growth retardation than in control infants. It increased slowly in groups A and B to reach the control values at age 9 and 12 months. In group C it remained significantly subnormal at 1 yr of age. Thymidine activity was also significantly lower at age 5 days in intrauterine growth retardation compared with control infants. It increased sharply at age 1-3 months in groups A and B but remained significantly lower in group C up to 1 yr of age. Although individual values of insulin-like growth factor 1 and thymidine activity were closely correlated, the increase of length during the first postnatal year correlated significantly with the thymidine activity levels at 1 and 3 months but not with the insulin-like growth factor 1 levels at 1, 3, and 6 months.(ABSTRACT TRUNCATED AT 250 WORDS)