LONDON (Thomson Reuters Foundation) - About one in five young women and girls in Kyrgyzstan are kidnapped for marriage, according to a study published on Wednesday which found their babies are smaller than average, probably due to their mothers’ psychological distress.

Bride kidnapping, which also occurs in countries like Armenia, Ethiopia, Kazakhstan and South Africa, is particularly common in rural parts of the Central Asian country even though it is illegal, researchers from the U.S.-based Duke University said.

The practice, known as “ala kachuu” which means “to take and run away”, involves a potential groom forcibly taking a young woman or girl back to his home before pressuring her to agree to marriage by writing a letter of consent and wearing a “marriage scarf” over her head.

In many cases, the groom will rape his kidnapped bride to prevent her from returning to her family due to shame, according to the United Nations Population Fund.

“After kidnapping, these women are no longer assumed to be virgins. In addition, they might be perceived as stubborn and belligerent if they resist the marriage ... (and) become less attractive to other potential suitors,” the report said.

Between 16 and 23 percent of women in Kyrgyzstan are abducted for marriage, but the rate is much higher among ethnic Kyrgyz where a third of all marriages are due to kidnapping, it said.

Ethnic Kyrgyz make up 70 percent of the country’s 6 million population which also includes Uzbeks, Russians and Turks.

Kidnapped brides tend to be younger than those in love marriages or arranged marriages, with 19 being the mean age, the study found.

Nearly one in 10 girls in Kyrgyzstan are married before they turn 18, according to global charity Girls Not Brides.

Although Kyrgyzstan outlawed bride kidnapping in 2013 and banned child marriage in 2016, nearly 12,000 young women and girls are thought to be kidnapped for marriage each year, the Women’s Support Centre in Kyrgyzstan says.

The study, published in the journal Demography, also said babies born to kidnapped brides weighed 80 to 190 grammes less than those from arranged marriages. Smaller birth weights have been linked to a higher risk of disease, lower education rates and earnings, it said.

It was unclear why these babies were smaller, but it was likely due to the psychological trauma suffered by the mother from being in a forced marriage, said economics professor Charles Becker, who co-authored the study.

There also seemed to be an underlying tolerance for bride kidnapping even though it is illegal, he added.

“The stigma of having been kidnapped does not seem to be large among the Kyrgyz, and people are willing to discuss it openly, even with strangers,” Becker said in a statement.

“Our next step is to explore why the practice of kidnapping is unofficially accepted in a country that quite recently had a woman president.”

About 15 million girls a year are married before the age of 18, Girls Not Brides estimates.