2. Materials and Methods
Using the “Preferred Reporting Items for Systematic Reviews and Meta-Analyses” (PRISMA) 2009 guidelines, a comprehensive search independently using two databases, namely OVID/Medline and PubMed, was performed for the keywords: “sexual dimorphism”, “sex differences “, “gender difference”, ”brain”, “infants”, and “neonates”. Keywords were combined using the Boolean operators OR and AND. The search strategy was as follows: (“sexual dimorphism” OR “sex differences” OR “gender differences”) AND (brain) and (“infants” OR “neonates”). All the keywords were used as exploded medical subject headings (MeSH) for the OVID/Medline and Pubmed. This study addressed studies published in peer-reviewed journals from 1945 p to 31 October 2022. All duplicates were excluded in addition to abstracts, case reports, non-English articles, reviews, commentaries, and editorials. All English studies published in any year about sexual differences in neonates’ and infants’ brains were included. Bibliography lists from all eligible articles were also hand-searched to identify additional papers potentially relevant for inclusion. No date restrictions had been set for the articles to be retrieved from the search. A total of 568 records were found in the literature related to brain sex differences. Of these, 208 studies did not meet our eligibility criteria and were excluded. Finally, a total of 36 full-text studies were included in our systematic review (Figure 1).