(November 2008) A new study in Proceedings of the National Academy of Sciences reports on a sex ratio that favors boys among U.S.-born children in Indian, Korean, and Chinese families. Using the 1990 and 2000 decennial censuses, the study found that the ratio of male to female births is much higher if the first child is a girl and even higher, by as much as 50 percent, if the first two children are girls. The normal ratio of males to females at birth is 1.05:1. However, if the first child is a girl, the ratio increases to 1.17:1, and if the first and second children are girls, the ratio increases more dramatically to 1.51:1 in favor of boys. The authors note that this is not evident with white parents and that the trend among the base group was not evident in the 1990 census.

The phenomenon is not unique to Asian immigrants in North America. In 2007, an Oxford University study suggested a similar phenomenon among Indian-born mothers in both England and Wales. It found that the proportion of male to female newborns increased from 103 male births per 100 female births in the 1970s to 114.4 by the end of 2005.

The authors expect the sex ratio to move upward given the recent surge in immigration from Southeast Asia and the availability of new technology that makes sex determination possible within the first five weeks of pregnancy. New reproductive technologies used for sex selection such as embryo screening, sperm sorting, and blood tests have been marketed to Indian expatriates in the United States and Canada in recent publications such as India Abroad and The Indian Express.

Given the small size of the Asian-born population relative to the total U.S. population, the practice is unlikely to have major consequences on the national sex ratio at birth in the short term. However, the implication of such practices might have a profound effect beyond U.S. borders. Since 1994, laws have been in enacted in India banning the use of embryo screening, sperm sorting, and other methods for sex selection, although these are not always strictly enforced. Canada, the UK, China, and the Council of Europe’s Convention on Human Rights and Biomedicine have all outlawed and condemned any type of sex selection method. However, the U.S. fertility industry remains largely unregulated and American Society of Reproductive Medicine recommendations on the ethical use of the technology are largely ignored by practitioners.

Nadwa Mossaad is research associate, Domestic Programs, at the Population Reference Bureau.


  1. Douglas Almond and Lena Edlund, “Son-Biased Sex Ratios in the 2000 United States Census,” Proceedings of the National Academy of Sciences 105, 15 (2008): 5681-82.
  2. BBC News, “UK Indian Women ‘Aborting Girls’,” accessed online at http://news.bbc.co.uk/2/hi/uk_news/7123753.stm, on Nov. 17, 2008.