PROMINENTLY displayed on the walls in the maternity ward of a Baoting county hospital, a sign reads: 'Scanning to determine the sex of your baby is illegal.'

But farmer Cheng Kongxian, 32, tells The Straits Times that a S$4 'red packet' is all it takes for some doctors and nurses to tell you if you are going to get a son or daughter.

He should know - he did exactly that when his wife was pregnant.

They have two sons, aged three and five, but Mr Cheng refuses to say if his wife ever had an abortion to get rid of an unwanted girl.

However, he lets on that it is common for couples turning to retired doctors to abort female foetuses for as little as 100 yuan (S$20).

Officially, sex-selective abortions are banned in China. On Hainan island, women cannot abort their babies except on medical grounds, such as when the pregnancy endangers the mother's life.

Ms Li Ping, vice-chief of the Hainan Province Population and Family Planning Office, says: 'You can use the ultrasound machine to find out if your baby is healthy, but not to find out the sex of your baby.'

Doctors caught performing sex-selective abortions risk, among other things, being fined and struck off the medical register.

Ms Li adds that a number of doctors have been caught in recent years and one was even jailed for a year.

That, however, has not stopped many Chinese doctors out to make a quick buck, says Beijing University demographer Li Yongping.

Many clinics stock ultrasound machines and doctors can recoup the cost of such a machine - introduced into the country in the late 1970s - after performing just 20 ultrasound scans.

To avoid getting caught for revealing the sex of a baby, doctors resort to sign language with their patients.

Prof Li, who did a study of the gender imbalance problem in Hainan two years ago, tells The Straits Times: 'If it's a baby boy, the doctor will nod his head. If it's a girl, the doctor will shake his head. No words are exchanged at all.'

He says that many Hainan women think it is a problem if they are going to have a girl.

'If the woman doesn't give birth to a son, she can't hold her head up,' he adds. 'People will mock her, saying that she doesn't even know how to give birth.'