Aims: There is a rapid rise in the male-to-female sex ratio at birth in Hong Kong, which coincides with the influx of Mainland Chinese mothers crossing the border to give birth in Hong Kong. Our objective is to explore the sex ratio patterns among Hong Kong Chinese and Mainland Chinese.
Methods: Analysis of the statistics from Hong Kong public hospitals from 2003 to 2007.
Results: For the 194,602 babies studied, 140,962 (72.4%) were eligible (Hong Kong Chinese) and 52,741 (27.1%) were non-eligible (Mainland Chinese). The overall sex ratio at birth (defined as males per 1000 females) was 1088; 1078 for eligible and 1116 for non-eligible. For eligible persons, the sex ratios were 1060 for parity 0, 1073 for parity 1 and 1184 for parity 2 or above. For non-eligible persons, the sex ratios were 1047 for parity 0, 1149 for parity 1 and 1745 for parity 2 or above. Non-eligible persons of parity 1 or above were more likely to have sons than eligible persons of same parity (P<0.000).
Conclusion: We believe that the rapid rise of sex ratio in Hong Kong can be partly explained by the influx of Mainland Chinese who may have practiced sex selection more than Hong Kong Chinese.