carbon monoxide in large urban areas and the number of newborn babies with serious heart defects, a study by the University of California, Los Angeles, published in 2002, provided the first compelling evidence that air pollution in cities may play a role in causing some birth defects.

Chinese medical experts have also conducted studies on the relationship between air pollution and birth defects. Xia Jianhong, a Ph.D. with the Guangdong Women and Children's Hospital and Health Institute, began to research the link between the environment and health in 2005, including subsidiary studies on air pollution and birth defect rates. She studied data on changes in birth defect rates in Guangdong Province and found that rates in rural areas had remained stable while cities with poor air quality, especially those with ongoing industrialization, had experienced steep spikes. She told Guangzhou Daily in September 2005 that one of her conclusions was that climbing numbers of birth defects and air pollution in cities are interrelated.

A trend for later pregnancies has also become a major factor behind congenital defects, said Professor Li Zhu, Director with the National Center for Maternity and Infant Health. He said women who give birth over 35 face greater risk of their babies being born with mental or physical defects. Many Chinese couples, especially urbanities, wait until their 30s to have a child because of heavy work pressures and fast-paced lifestyles.

Controversial pre-marital checks

Many experts hope that the reinstatement of compulsory pre-marital health checks that was abolished nationwide in 2003 can help curb the rising numbers of birth defects in parts of China.

The southern province of Guangdong has experienced high levels of thalassemia, one of the most common genetic diseases in the world. About 11 percent of the population in the area carries the thalassemia gene. If both parents carry it, their children have a 25-percent chance of becoming victims of senior thalassemia (a severe life-threatening form of the condition). These babies either die shortly after birth or develop symptoms at a young age, which can only be cured by an expensive bone marrow transplant or cord blood transplant.

Although the province added thalassemian gene screening to pre-marital checks in 1999, the monumental drop of pre-marital checks has effectively handicapped this policy. From 2002 to 2004, the proportion of couples conducting pre-marital checks slid from 62.4 percent to 2.9 percent while over the same period the birth defects rate surged from 1.372 percent to 2.121 percent.

Shenzhen City in Guangdong Province started to provide free pre-marital checks from 2005 and realized totally free pre-marital counseling in all city districts in 2007. Yet enthusiasm remains low with the best district registering a participation rate in pre-marital checks of just 25 percent.

In June 2005, Heilongjiang in northeast China became the first province to resume compulsory pre-marital checkups.

Ma Huaide, a professor at China University of Political Science and Law, explained in an online forum for news website peopledaily.com.cn that most people are against compulsory pre-marital tests because of their ineffectiveness, cost and out of the fear that they could breach their privacy.

According to professor Wang Yifei, former Dean of Shanghai Jiao Tong University's School of Medicine, 50-60 percent of birth defects occur for no obvious reason. Wang's research revealed that, chromosomal abnormality contributes to 6-7 percent, genetic mutation contributes 7-8 percent, environmental factors 7-10 percent and the comprehensive effect of hereditary and environment factors 20-25 percent, of birth defects.

Wang said for the prevention of birth defects, China needs to establish a monitoring system linked with an international network, and step up research on hereditary and environmental factors.