The Health Bureau of Beijing has urged couples to take pre-marital medical tests to prevent the spread of sexually transmitted diseases and help reduce the rate of birth defects.

Less than 10 percent of newly wed couples in the city have taken pre-marital medical tests, the bureau said.

The rate was 100 percent before 2003, when the city's government stopped mandatory medical tests before marriage, according to the bureau.

The rate of birth defects in Beijing, such as cleft palates, congenital heart disease and intellectual disability, has risen as the number of couples getting pre-marital tests dwindled, the bureau said.

The incidence of syphilis during pregnancy in Beijing is also on the rise, which the bureau said is relevant to the low test rate.

In 2007, Beijing stopped charging fees for pre-marital medical tests in order to encourage more couples to take them.

This year, pre-marital medical tests have added tests for HIV.

Nationwide, the incidence of birth defects is 5.6 percent - about 900,000 of the 16 million babies born every year are born with defects, according to a report issued by the National Health and Family Planning Commission in 2012.

However, Huang Yu, deputy director of the genetics department of the Peking University Health Science Center, believes pollution and mutation are among the main causes of the increase of birth defects.

He said pre-marital tests plays a limited role in preventing birth defects, because the likes of cleft palates and congenital heart disease can only be detected during pregnancy. If a fetus has certain defects, a woman may also be advised to undergo an abortion.

He also said pre-marital tests may not show recessive genes that could cause birth defects.

"Mediterranean anemia is an exception, because there are so many people carrying genes that can cause this defect in some provinces that it's cost-effective to screen couples in these areas for the gene, so the disease is not passed on to their children," he said.

"But it would be too costly to include tests for many other kinds of defects into the pre-marital medical tests because they occur rarely."

South China's Guangdong province and Guangxi Zhuang autonomous region have included tests of the genes for Mediterranean anemia in pre-marital tests.