Fetal growth in relation to maternal and fetal IGF-axes: a systematic review and meta-analysis.

Insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) are key regulators of fetal growth. However, the literature is inconsistent. Our objective was to systematically and objectively evaluate the available literature and to develop a balanced opinion on the relation between maternal and fetal IGF-axes and birthweight. A systematic review and a meta-analysis were conducted according to the published Moose (Meta-analysis of Observational Studies in Epidemiology) guidelines. A robust recognized systematic methodology was used in the literature search and analysis to avoid bias. Weighted mean difference and 95% confidence intervals of cord/maternal IGFs and IGFBP-1 and -3 were calculated. Eleven observational studies were included. Cord IGF-I (p < 0.0001) and IGFBP-3 (p = 0.003) were significantly higher in large-for-gestational age (LGA) than appropriate-for-gestational age (AGA) babies. Cord IGFBP-1 was significantly higher in small-for-gestational age (SGA) than AGA babies (p < 0.0001). LGA and AGA babies had similar IGF-II levels, whereas SGA and AGA babies had comparable IGF-I levels. IGF-I was significantly higher in mothers of AGA than SGA babies (p < 0.0001). The assay methods and background population marginally affect the overall homogeneity and the direction of the primary analysis. Fetal IGFs and their binding proteins play different roles in fetal growth at either end of the growth spectrum. Fetal IGF-I and IGFBP-3 may be influential in LGA. However, fetal IGFBP-1 has a more prominent role in SGA.