Almost half of female migrant workers under 30 have become pregnant before marriage, a dramatic jump in the number of unwed mothers compared with only a generation ago, according to a report on the migrant population's changing behavior in sexual and marital affairs.

Experts warn that increased pregnancy before marriage may result in more violations of women's rights.

The report, based on monitoring results of migrant workers in 2011 and released by the National Population and Family Planning Commission, said nearly 43 percent of second-generation female migrant workers got pregnant before getting married, 16 percentage points higher than their counterparts of older generations.

The report defines migrant workers born in the 1970s and earlier as the first generation and those born later as the second generation.

The second generation of migrant workers marry later in life compared with their older counterparts, according to the report. It showed only about 35 percent got married before the age of 23, 15 percentage points lower than the first generation.

Increasing numbers of younger migrant workers get married after migration. The report said more than half of those married did not wed in their home villages, double the number of their older counterparts.

Jiang Yongping, a researcher at the Women's Studies Institute of China in Beijing, attributed the changes to the fact Chinese society is now more open to sex before marriage and unwed couples living together.

However, Jiang said the high rate of pregnancy outside marriage among migrant workers also indicates that China should work harder to educate this group about safe sex and popularize measures of contraception.

Chen Wei, a lawyer at Beijing Yingke Law Firm specializing in marital affairs, said on Tuesday she has noted an increase in legal disputes related to pregnancy before marriage. Chen warned that women's rights are more vulnerable in cases where they get pregnant before marriage.

"It's very difficult to ask the child's father to give child support without official marriage registration in cases where the couple break up," she said.

"Some women resort to abortion, which hurts their health in varying degrees and in extreme cases can result in infertility."

hedan@chinadaily.com.cn