Sources of bias in studies reporting birth prevalence of congenital anomalies: a scoping review and reporting checklist.

Background: Data on the birth prevalence of congenital anomalies in low- and middle-income countries report wide variations in prevalence estimates. We conducted a scoping review to identify the sources of bias in studies reporting birth prevalence of congenital anomalies in World Health Organization South-East Asia region (SEAR) countries.

Methods: PubMed and Google Scholar databases were screened for relevant literature. Data on study characteristics and sources of bias was extracted. A narrative synthesis of the data is reported using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews checklist. A checklist for reporting studies on birth prevalence of congenital anomalies (CD-Checklist) was developed.

Results: The literature search retrieved 47 articles. Birth prevalence varied from 0.21% to 9.68%. Sampling bias was evident as studies were single hospital studies, lacked relevant description of sample, did not justify sample size or describe the process of sampling. Information bias was identified as studies did not mention classification system used, and failed to clearly distinguish between number of malformations and babies with malformations. Observer and reporting bias were noted.

Conclusions: Several sources of bias introduce variations in birth prevalence reports of congenital anomalies in SEAR countries. A checklist (CD-Checklist) has been suggested which can guide investigators to minimize the risk of bias in studies.