Nguyen MV, et al. - Researchers examined the link between birth order and childhood brain tumors (CBT), via a systematic review and meta-analysis. They identified relevant English language studies which were published before March 2018 in Ovid Medline, PubMed, and the Cochrane Library. This analysis included 16 case–control studies including 32,439 cases and 166,144 controls and three prospective cohort investigations (ie, 4,515 incident cases of CBTs in 5,281,558 participants). In case–control studies, the meta-odds ratio for second birth order vs first birth order was estimated to be 1.04, this value was 0.98 and 0.85 for third birth order and for fourth order, respectively. Compared with first birth order, the meta-hazard ratio for second or higher birth order was estimated to be 1.00 in cohort studies. In both case–control and cohort study designs, findings revealed no link between birth order and CBT; a small link was observed for fourth birth order which requires further consideration.