A meta-analysis of relationship between birth weight and cord blood leptin levels in newborns.

CONTEXT Low cord blood leptin concentration is implicated as a risk factor for small for gestational age (SGA) babies. However, the association of strength, consistency, independence, and confounding factors of this affliction has not been systematically examined. OBJECTIVE To determine if there is a difference in cord blood leptin concentration between SGA and appropriate for gestational age (AGA) newborns, and to observe whether the sample origins, GA, pregnancy-induced hypertension (PIH) and congenital malformation (CM) are confounding factors of the meta-analysis. DATA SOURCES AND STUDY SELECTION Relevant studies published between 1996 and 2007 were identified through literature searches using Ovid, Medline, PubMed, Web of Science, National Knowledge Infrastructure, Wanfang Data, and VIP China Scientific Journal Database, based on the following key words: leptin, intrauterine growth restriction, intrauterine growth retardation, fetal growth restriction, and small for gestational age. DATA EXTRACTION A meta-analysis was conducted to analyze the difference of the cord blood leptin concentrations between SGA and AGA newborns. Then the stratified meta-analyses were repeated with a multivariate model to adjust for potential confounders, i.e., samples origin (Chinese newborns vs. non-Chinese newborns), GA (the term-newborns vs. the mixed GA newborns), PIH or CM (the newborns excluding PIH or CM vs. the newborns not excluding PIH or CM). DATA SYNTHESIS Twenty articles including 514 SGA newborns and 1006 AGA newborns were collected. The cord leptin concentrations of SGA newborns were lower than those of AGA newborns [WMD (95%CI), -4.42 (-5.54, -3.29) ng/ml; P<0.01; n=1520 newborns]. The results of stratified meta-analyses showed similar results in Chinese vs. non-Chinese newborns and term vs. mixed GA newborns, respectively. However, the newborns not excluding PIH or CM had a wider 95%CI than the newborns excluding PIH or CM [WMD (95%CI), -4.17 (-5.00, -3.33) ng/ml vs. -4.47 (-9.61, 0.67) ng/ml)], and there was no significant difference in cord blood leptin concentrations between SGA and AGA newborns in the newborns not excluding PIH or CM (P=0.09). CONCLUSIONS SGA babies have low cord leptin concentrations. Other factors that may influence cord leptin levels are maternal PIH and CM.