As assisted reproductive technologies improve, Nanjing, the capital of East China's Jiangsu province, is seeing the number of twins delivered at local hospitals nearly double the number of five years ago, Nanjing Daily reported on Friday.

In natural pregnancies, there is on average one set of twins born for every 89 births, but the current birth rate for twins is far higher, according to Ling Xiufeng at the Nanjing Maternity and Child Health Care Hospital. Besides, nearly one third of test-tube babies are twins, according to Ling.

The number of couples who receive fertility treatment at her hospital is growing by 30 percent each year, while it completed more than 3000 embryo transfers last year alone, she said.

Wang Pei, Ling's colleague at the hospital, said that another reason for the rising number of twins is that some healthy women, who desire twins, secretly take ovulation induction drugs.

Large hospitals strictly control the use of such drugs, though some smaller medical institutions, motivated by economic interests, may abuse these medications, it was added.

The doctor warns that improper use of ovulation induction drugs could result in a series of health risks for women, which can even be life-threatening.