Sex ratios at birth in Australia according to mother's country of birth: A national study of all 5 614 847 reported live births 1997-2016

Objectives Son preference and sex selective practices have resulted in a deficit of girls in several countries, primarily across Asia. Emerging evidence indicates that son preference survives migration to Western high-income countries. The objective of this study was to assess male-to-female (M/F) ratios at birth per mother's country of birth in Australia 1997-2016, in total and by parity, and by states/territories and over time. Methods Data for this national population-based cross-sectional study were obtained from the National Perinatal Data Collection (NPDC) and included all live births in Australia 1997- 2016 (N = 5 614 847). M/F ratios with 95% Confidence Intervals were estimated. Results The M/F ratio for births to Australian-born mothers was within the expected range (1.03- 1.07) regardless of parity and time period. M/F ratios were elevated above the expected range for births to mothers born in China in the total sample (M/F ratio 1.084, 95% confidence interval 1.071-1.097) and at parity 2 (1.175, 1.120-1.231), and for births to mothers born in India at parity 2 (1.146, 1.090-1.204). Parity 2 births were the most consistently male-biased across time. Across states, elevated M/F ratios were identified for both groups in New South Wales (China parity 2: 1.182, 1.108-1.260; India parity 2: 1.182, 1.088- 1.285), for births to Chinese-born mothers in Victoria (total births: 1.097, 1.072-1.123; parity 1: 1.115, 1.072-1.159) and Australian Capital Territory (total births: 1.189, 1.085-1.302) and births to Indian-born mothers Western Australia (parity 2: 1.307, 1.122-1.523). Conclusions Son preference persists in some immigrant communities after migration to Australia. The consistent pattern of elevated M/F ratios across the larger states indicates that sex imbalances at birth are largely independent of restrictiveness of local abortion laws. Drivers and consequences of son preference in Western high-income settings should be explored to further promote gender equality, and to strengthen support for women who may be vulnerable to reproductive coercion.