A preference for sons in those countries, combined with easy access to sex-selective abortions, has led to a significant imbalance between the number of males and females born there, an article in the Canadian Medical Association Journal reported Monday.
The sex ration at birth worldwide is consistent at about 105 boys born for every 100 girls, but with the advent of ultrasounds that enable sex-selection, the sex ratio at birth in some cities in South Korea climbed to 125:1 by 1992 and is above 130:1 in several Chinese provinces from Henan in the north to Hainan in the south, the article said.
In 2005 in China, "it was estimated that 1.1 million excess males were born across the country and that the number of males under the age of 20 years exceeded the number of females by around 32 million," Therese Hesketh at University College London said.
The imbalances mean a significant percentage of the male population will not be able to marry or have children because of a scarcity of women, the researchers said.
Authorities in China, India and South Korea have taken some steps to address the problem, such as instituting laws forbidding fetal sex determination and selective abortion, but more can be done, the article said.
"To successfully address the underlying issue of son preference is hugely challenging and requires a multifaceted approach," the authors said.