'Maternity migration' and the increased sex ratio at birth in Hong Kong SAR.

The sex ratio at birth (SRB) in Hong Kong SAR (Special Administrative Region) has recently increased dramatically. Using a data set (N = 850,331) of all recorded births in Hong Kong between 1995 and 2009, we calculated SRBs by parity and immigrant status. The findings indicate a strong son preference among Mainland Chinese who have travelled to Hong Kong to give birth, especially at parity two or above. Logistic regression models show that this tendency is significantly greater among more affluent couples and remains strong even among Mainland Chinese women resident in Hong Kong for any length of time. The SRB of Hong Kong-born couples, though elevated at higher parities, is less skewed. Hong Kong has been serving as an outlet for 'elite' Mainland couples to circumvent family planning restrictions. The analysis also suggests the advantages of a wider set of immigrant variables over a binary construct.