Although the country bans ultrasound scans to distinguish infants' gender, it still occurs.
"Some private practicing doctors and small hospitals are providing this illegal service. In recent years, the services have become very sophisticated and gender scans can be arranged at the client's home," Zhai said, adding that it was very difficult to catch the offenders.
Prof. Yuan Xin, director of the Population and Development Institute of Nankai University in Tianjin, said stopping discrimination against women will help curb the sex ratio imbalance.
"Chinese women still lag behind men in career development, political life and in family life, except for the education level," he said.
"If women's social status improves, parents will feel better about raising a female child," he said.
A report issued by the Chinese Academy of Social Sciences last December estimated that China's male population at marriageable age will be 24 million more than female counterparts in 2020.
