The rate of multiple births for mothers who receive fertility treatments is higher than 20 percent in some areas of China, the top health authority said in an exclusive email exchange with China Daily.

The National Health and Family Planning Commission also warned of the potential health risks facing both the mother and babies from a multiple pregnancy and birth.

Experts say the incidence of twins through natural pregnancy is only 1 percent, and triplets or more are much rarer.

In China, wider application of assisted reproductive technologies, such as in vitro fertilization, has swelled the number of artificially induced multiple births.

However, "it can bring health risks for a mother and her babies, such as anemia, womb damage, premature birth and birth defects," said Wang Aiming, a professor of assisted reproduction who used to work at the Navy General Hospital and now works for a private clinic.

She said that during an IVF procedure, usually more than one embryo is transferred to the womb of a patient to increase the chances of a successful pregnancy.

"If two embryos are transferred, usually at least one becomes a successful pregnancy at many hospitals in Beijing," she said. "In some hospitals, more than 40 percent of women who have two embryos transferred have both of them become successful pregnancies."

To regulate the use of assisted reproductive technologies to control the incidence of multiple pregnancies, the national health authority has released regulations requiring patients receiving artificial insemination to sign documents before their procedure agreeing to have one or more embryos removed if multiple successful pregnancies occur.

For each IVF procedure, no more than three embryos can be transferred to the womb of a patient, while no more than two are allowed for women under 35 who are having IVF for the first time, according to existing regulations.

However, most doctors, Wang said, follow the patient's wishes to allow both twins to be born. "But for triple pregnancies, usually we will persuade the parents to have one embryo removed."

Qin Lang, a doctor in reproductive medicine at West China Second University Hospital in Chengdu, Sichuan province, said with the development of technology, more hospitals in China are trying to transfer only one embryo during each IVF procedure, as in most cases the embryo survives.

"Multiple pregnancies with IVF are risky for both mother and babies, and should be avoided when possible," he said. "So the trend in the future is for each IVF procedure, only one baby is born."

In the United States, there are laws that limit the number of embryos that can be transferred during one procedure to up to two, according to Cameron Hou, chief representative for China at the California Center for Reproductive Health.

"In most cases doctors transfer only one embryo, and the success rates of birth can be as high as 70 percent," he said.

James Marshall, senior geneticist of Superior ART, an institute of assisted reproductive technology in Bangkok, Thailand, that treated about 600 Chinese clients last year, said that in Thailand there are no laws regulating the number of embryos that can be transferred during IVF procedures. Doctors, however, generally believe it best to transfer only one during a procedure, he said.

"In our institute, doctors transfer only one embryo for an IVF procedure in most cases," he said. "Having twins or triplets through an IVF procedure can increase all risks for mothers and babies during natural birth by several times."

Nationwide, China performs on average 700,000 IVF procedures a year, according to the National Health and Family Planning Commission.

The country has an estimated 40 million infertile couples - those who are unable to have a pregnancy naturally after trying for six months. Roughly 20 percent need fertility treatment, the authority said.

However, in recent years, the treatment appears to have been abused, Wang said. "That brings health concerns for the women. Some couples, who do not need IVF for pregnancy, ask doctors to prescribe drugs to facilitate ovulation in the hope of getting pregnant with twins, and some doctors may prescribe such drugs against regulations," she said.

Those drugs should be used only when necessary in assisted reproductive technologies such as IVF, experts said.

Wang suggested the health authority strictly correct the abuse of such drugs.

The national health commission said in the email response to China Daily that it will improve management of ovulation-facilitating drugs, and better regulate their supply and distribution to prevent them from being used improperly.