MATERNAL INSULIN SENSITIVITY AND CORD-BLOOD PEPTIDES - RELATIONSHIPS TO NEONATAL SIZE AT BIRTH

Objective: To examine the relationship of multiple maternal and cord b lood correlates of newborn size to determine the relative strength of the insulin-like growth factor-I association. Methods: Thirty-seven ve nous cord blood specimens were obtained;It the time of delivery. Ponde ral index and birth weight percentile were calculated at birth. Neonat al length estimates were performed with a measuring board. All mothers were nonsmokers and had normal glucose tolerance. There was a wide ra nge of maternal prepregnancy body mass indexes (BMI) (19.6-43.4). Neon ates had a wide range of ponderal indexes (2.12-2.75) and birth weight percentiles (7-99th percentile). Univariate correlation coefficients were calculated to determine simple relationships. Stepwise linear reg ression analyses were performed to determine the relative contribution of potential explanatory variables to both ponderal index and birth w eight percentile. Potentially explanatory independent variables includ ed maternal prepregnancy BMI, weight gain in pregnancy, and maternal i nsulin sensitivity at 32 weeks' gestation. Maternal insulin sensitivit y was estimated using the minimal model technique. Neonatal variables included sex, cord blood albumin, insulin, insulin-like growth factor- I, insulin-like growth factor-binding protein-1, and insulin-like grow th factor-binding protein-3. Results: Significant positive univariate correlations were identified between cord blood insulin-like growth fa ctor-I and insulin-like growth factor-binding protein-3 with neonatal ponderal index and birth weight percentile. Maternal insulin sensitivi ty demonstrated a negative correlation with birth weight percentile (r = -.35, P < .05). Cord blood insulin correlated positively with birth weight percentile (r = .32, P < .05). There were no significant assoc iations of cord blood insulin-like growth factor-binding protein-1 or albumin with either index of newborn size. Stepwise logistic regressio n analysis demonstrated an independent association of insulin-like gro wth factor-I with ponderal index (r(2) = .41, P < .001). Both insulin- like growth factor-H and male sex were associated independently with b irth weight percentile (r(2) = .38, P < .001). No additional independe nt variables contributed to the prediction of ponderal index or birth weight percentile. Conclusion: These data support a unique relationshi p between cord blood insulin-like growth factor-I and newborn size und er normal growth conditions. This is manifest by the strength and inde pendence of the association between insulin-like growth factor-I and n eonatal birth weight percentile ponderal index. (C) 1997 by The Americ an College of Obstetricians and Gynecologists.