The New York Times reports that economists at Columbia and the University of Texas have found strong evidence that many American parents of Chinese, Korean, and Indian descent use various sex selection methods to make sure they have at least one boy:
In general, more boys than girls are born in the United States, by a ratio of 1.05 to 1. [Girls have a better survival rate.] But among American families of Chinese, Korean and Indian descent, the likelihood of having a boy increased to 1.17 to 1 if the first child was a girl....If the first two children were girls, the ratio for a third child was 1.51 to 1—or about 50 percent greater—in favor of boys....
On the basis of census and birth records through 2004, the incidence of boys among immigrant Chinese parents in New York was higher than the national average for Chinese families. Boys typically account for about 515 of every 1,000 births....Among Chinese New Yorkers having a third child, the number of boys was about 558.
Notably, the gender imbalance at birth is much more dramatic in China, where 120 boys are born for every 100 girls. That's the overall rate, not (as in the American research) the rate for families that already have a girl. Sex-selective abortions, though illegal in China, are the preferred method for getting a boy/avoiding a girl there, whereas Chinese Americans also use in vitro fertilization or sperm sorting. While acculturation and economic improvement may partly explain why immigrants from China are more likely to have girls than parents who remain there, the country's strict population controls surely have much to do with it. When parents are limited by law to one or two children (depending on where they live), they are more likely to take extraordinary measures to ensure that the first or second is a boy. The combination of a preference for boys and the "one child" policy also leads to widespread abandonment of baby girls in China.
A couple years ago, I explored the nexus between China's population policy and international adoption in "Thank Deng Xiaoping for Little Girls."