The rate of birth defects in China is rising rapidly, almost doubling over the past decade in Beijing with sharp increases in several other provinces.

The capital's rate of birth defects last year was 170 per 10,000 births, nearly twice the rate of 90 per 10,000 in 1997, the Beijing municipal health bureau has announced.

"The higher incidence is mainly because diagnostic techniques and monitoring capability have improved, as well as more and more women are delaying having children," Beijing Daily quoted an anonymous officer with the Beijing health bureau.

Environmental pollution could also be contributing to the soaring rates, Caijing magazine reported.

"Chemical and toxic emissions impact the health of the parents, so it is likely they also impact the health of an unborn baby," said Ren Aiguo, director of the reproductive health institute at Peking University.

Also, in 2003, authorities canceled mandatory premarital health check-ups in order to protect the privacy of newlyweds, which some experts believe is another cause, the magazine reported.

The most common birth defects in Beijing's Shunyi district include congenital heart disease, excessive numbers of fingers or toes, cleft lip or palate, and neural tube defects, said Wang Haiying, an officer with the family planning and reproductive health service center in the district.

China's rate of birth defects is high compared to other countries, with about 4 to 6 percent of the 20 million newborn babies having birth defects, it said. Three to 4 percent is considered a baseline rate caused by naturally occurring defects.

Outside the capital, other provinces saw sharp increases in birth defects over the past decade, Caijing magazine reported. In Zhejiang province, the rate in 2003 was 115 per 10,000, but increased to 208 in four years. In Hunan province, the rate was 91 per 10,000 in 2001 and rose to 166 cases in five years. In Jiangxi province, the rate of 102 cases per 10,000 people in 2000 rose by about 50 percent in six years.

In Guangdong province, birth defects increased to 249 cases from 186 per 10,000 between 2003 and 2007.