Mai V. Nguyen 1* , Mo T. Tran 1* , Chi TDu Tran 1 , Quang H. Tran 1 , Van Thuy TT 1 ,
Lam N. Phung 1 , Huyen X. Vu 1 , Linh C. Le 1,2 , Paolo Boffetta 3¶ , Hung N. Luu 4,5,6¶
1 Vietnam Colorectal Cancer and Research Program, Vinmec Healthcare System, Hanoi, Vietnam; 2 VinUniversity Project - Health Sciences, Hanoi, Vietnam; 3 Tisch Cancer Institute, Icahn School of Medicine, Mount Sinai School of Medicine, New York, NY; 4 Division of Epidemiology, Department of Medicine, Vanderbilt Epidemiology Center, Vanderbilt-Ingram Comprehensive Cancer Center, Vanderbilt University School of Medicine, Nashville, TN, USA; 5 Department of Epidemiology, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA, USA; 6 Division of Cancer Control and Population Sciences, University of Pittsburgh Medical Center-Hillman Cancer Center, Pittsburgh, PA, USA
* First author
¶ Senior author
Background: With the improvements of early diagnostics, the incidence of childhood brain tumors (CBT) has increased worldwide. We conducted a systematic review and meta-analysis to clarify the association between birth order and CBT.
Methods: We followed established guidelines to systematically search Ovid Medline, PubMed, and the Cochrane Library for English language studies, published before March 2018. Quality assessment was performed using the Newcastle–Ottawa Scale. Meta-analysis provided pooled risk estimates and their 95% confidence intervals (CIs) for birth order and CBT.
Results: We identified 16 case–control studies with a total sample of 32 439 cases and 166 144 controls and three prospective cohort studies (i.e. 4515 incident cases of CBTs among 5 281 558 participants). Compared with first birth order, the meta-odds ratio for second birth order in case–control studies was 1.04 (95% CI: 1.01–1.07), that for third birth order was 0.98 (95% CI: 0.90–1.06), and that for fourth order was 0.85 (95% CI: 0.78–0.92). The meta-hazard ratio for second or higher birth order compared with first birth order in cohort studies was 1.00 (95% CI: 0.96–1.05).
Conclusion: We found no association between birth order and CBT in both case–control and cohort study designs; the small association observed for fourth birth order deserves further consideration.
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