Retrospective study on the 'sex ratio at birth' in Western Sydney Local Health District between 2011 and 2020.

OBJECTIVE: Sex selection is not permitted in Australia; however, there are indirect means for such selection to occur, for example, through sex identification and the early termination of pregnancy. Indirect evidence for such selection, if any, may be inferred from variations in the 'sex ratio at birth' (SRB) among different populations. This study aims to characterise the SRBs over 11 years in spontaneous and assisted births in the largely migrant population of Western Sydney. DESIGN: This is a retrospective cohort study. SETTING: Western Sydney Local Health District over three maternity hospitals. PARTICIPANTS: A total of 109 931 births between 2011 and 2020, where gender was assigned at birth, were included in the study. PRIMARY AND SECONDARY OUTCOMES MEASURED: The primary outcome measured was the SRB between ethnicities and mode of conception. RESULTS: There was a higher male to female SRB for mothers born in China (SRB=1.12) compared with mothers born in Australia (SRB=1.05). Mothers from China were 1.1 times more likely to have a son. Otherwise, there was no significant difference with the SRB according to year, parity and mode of conception. CONCLUSION: Among the Western Sydney population, mothers born in China show a higher male SRB, reflecting a possible sex preference. However, this study is not without some limitations, for which purpose further study is warranted.