A systematic search of the factors that influence the sex ratio at birth

Abstract

Introduction: The sex ratio at birth has been studied for decades. A systematic review of the factors that influence this has never been performed. This study conducted a systematic search of this topic.

Methods: A scoping review of the literature was initially carried out in January 2012 and this was formally updated for contemporaneity in December 2017. A systematic search of the literature subsequently followed in May 2019 and was conducted based on PRISMA statement's flow diagram. The search was applied across five databases: Cumulative Index to Nursing and Allied Health Literature (CINAHL), MEDLINE, PubMed, The Cochrane Library and Web of Science and was restricted to January 1, 1990 to May 31, 2019. The systematic review stopped at screening stage of the PRISMA. A narrative approach was adopted to report study findings.

Results: 494 studies were included. Ten factors were identified from the literature as having an influence on M/F, with stress and sex-selective termination being the most predominant. Additional factors included the hormonal theory, geographical trends, coital rates, radiation, secular trends, seasonality and theoretical modeling.

Discussion: Future studies addressing M/F should adopt similar methodologies in order to provide the possibility of comparison between findings and a more formal form of systematic review.