From The Economist:

"Gendercide" is often seen as an unintended consequence of China’s one-child policy, or as a product of poverty or ignorance. The surplus of bachelors—called in China guanggun, or “bare branches”— seems to have accelerated between 1990 and 2005, in ways not obviously linked to the one-child policy, which was introduced in 1979. And, as is becoming clear, the war against baby girls is not confined to China.

The use of sex-selective abortion was banned in India in 1994 and in China in 1995. It is illegal in most countries. But since it is almost impossible to prove that an abortion has been carried out for reasons of sex selection, the practice remains widespread. An ultrasound scan costs about $12, which is within the scope of many—perhaps most—Chinese and Indian families. In one hospital in Punjab, in northern India, the only girls born after a round of ultrasound scans had been mistakenly identified as boys, or else had a male twin.