A population expert has urged the central government to make pre-natal sex selection a criminal offence because the mainland's gender imbalance has become one of the biggest in the world. Wei Jinsheng , a researcher with the China Population and Development Research Centre, wrote in an article carried by the latest issue of Qiushi (Seeking Truth), that the National People's Congress should incorporate a provision outlawing sex selection into the criminal law. There were 20 million more males than females under the age of 20 in 2004, Mr Wei wrote. Many men in poor and remote rural areas would not be able to get married, and such a phenomenon would seriously affect social development and stability. Government statistics showed that 117 boys were born for every 100 girls, compared to international averages of 104 to 107 boys per 100 girls, he added. Although pre-natal sex selection is banned on the mainland, it remains a common practice and an earlier attempt by some lawmakers to make it a criminal offence failed because of divided opinions, Xinhua reported. A draft amendment to the criminal law submitted to the NPC Standing Committee for review earlier this year suggested that sex-selective embryo screening should be punishable by three years in jail and a fine. But the draft did not get through because of objections from some lawmakers.