Household registration

The sexual revolution hasn't been the only driver of advanced DNA testing, though. In the past five years, the popularity of paternity testing has been boosted by the government's moves to strengthen the management of birth certificates. For the first time, the sixth national census, conducted in 2010, explicitly stated that children born outside the country's family planning policy, which limits most couples to one child, are eligible for hukou, a household registration certificate, but only if the parents can provide the results of a paternity test.

People in the cities are taking paternity tests because they've had a child in contravention of the family planning policy or outside marriage. However, for migrant workers whose children were delivered at home and therefore don't have a hospital birth certificate, the test is the only way of proving a blood relationship between parents and child. Without such proof, it's virtually impossible to obtain a permit that will allow the child to live in a prosperous area.

Figures from the institute show a huge rise in the number of parents taking paternity tests to obtain hukou for their children since 2009. "Nearly 70 percent of all DNA paternity testing is undertaken to obtain a certificate of parent-child ties," Deng said. "But unfortunately, around 1 or 2 percent of those tests have produced unexpected, or unwanted, results - that is, the child isn't the offspring of their nominal father."

According to Sun Liyang, director of the Xinjiang Forensic Authentication Institute, more than 80 percent of all paternity tests conducted by the institute are the results of private requests. Around 50 percent of the 300 tests conducted by the institute last year were motivated either by a desire to obtain hukou or because of suspicions about marital loyalty. Among those 300 tests, nearly 50 percent disproved the child-parent link. The number of requests has risen by 50 percent annually during the past three years.

While the proportion of requests from suspicious husbands has fallen, compared with the soaring number of tests conducted to determine paternity or to obtain hukou, pregnant women have gradually begun to account for a larger share of the business.

"They are looking for the baby's natural father," Deng said, adding that she recently dealt with an expectant mother who arrived at the test center accompanied by four men, because she didn't know which was the baby's father. Deng said cases such as this account for 5 to 10 percent of the total. Most female clients are married and have been pregnant for more than 16 weeks. "The number usually peaks during summer," she added.

The rise in the popularity of paternity testing is regarded by some as the inevitable byproduct of a more open society.

"It's understandable that people are losing confidence in loyalty in marriage because we've seen or heard about more one-night stands and cheating within marriage," an Internet user named "Little Apple" commented on her micro blog in relation to a news report about a man in the southwestern municipality of Chongqing who conducted a traditional paternity test on his son by mixing their blood in a bowl of water.