Birth weight and childhood wheezing disorders: a systematic review and meta-analysis

Background Previous observational studies have claimed that birth weight and childhood wheezing disorders are associated although the results remained inconsistent. One systematic review and two systematic reviews that included meta-analyses reported inconsistent results. We aimed to conduct a systematic review and meta-analysis to investigate this. Methods An online search of published papers linking childhood asthma and wheezing disorders with birth weight up to February 2014 was carried out using EMBASE and Medline medical research databases. Summary ORs were estimated using random-effects models. Subgroup meta-analyses were performed to assess the robustness of risk associations and betweenstudy heterogeneity. Results A total of 37 studies comprising 1 712 737 participants were included in our meta-analysis. The unadjusted summary ORs for risk of childhood wheezing disorders associated with low birth weight (<2.5 kg) were 1.60 (95% CI 1.39 to 1.85, p<0.001) and 1.37 (95% CI 1.05 to 1.79, p=0.02) when compared with >= 2.5 and 2.5-4.0 kg birthweight groups, respectively. The overall summary OR for high birth weight (>4 kg) as compared to the 2.5-4.0 kg birthweight group was 1.02 (95% CI 0.99 to 1.04, p=0.13). There was substantial heterogeneity in the unadjusted low birth weight risk estimates which was not accounted for by predefined study characteristics. There was no significant heterogeneity in the high birth weight risk estimates. There was some evidence of funnel plot asymmetry and small study effects in the low birth weight (2.5 vs >= 2.5 kg and <2.5 vs 2.5-4 kg) OR estimates. Conclusions Our results suggest that low birth (<2.5 kg) is an independent risk factor for wheezing disorders during childhood and adolescence although there was substantial heterogeneity among the risk estimates. However, we found no significant association of high birth weight with wheezing disorders.