Seven-month-old Cheng Jixiang, four months premature, is still hooked up to life-saving equipment but he's luckier than his twin sister who died two months ago.

He's now at home after receiving hyperbaric oxygen therapy and other treatment while in a hospital incubator. And there's feeding and medication. All of this costs thousands of yuan and surgery will come later when he is stronger, funded by a charity, Premature Baby Aid Fund.

Cheng was born with intestinal perforation, thyroid and other problems associated with insufficient development of organ systems.

Baby Cheng is an extreme case, but many premature babies face far more health problems than babies carried to full term. Premature babies are defined as those born after less than 37 weeks' gestation.

Worldwide, an estimated 13 million premature babies are born every year, around 10 percent of births, according to White Paper on Preterm Birth provided by the Department of Reproductive Health and Research of the World Health Organization. The rates vary widely among regions. Each year around 1 million babies die within the first month of life.

Rates are rising in many countries, including China.

The natural rate of premature delivery is around 7 percent but it has been increasing in recent years, especially in big cities such as Shanghai, Beijing and Guangzhou, Guangdong Province, says Ma Jianian, secretary general of the Premature Baby Aid Fund. The fund was first an association of parents and now provides lectures for parents and parents-to-be about premature babies and special care.

"Today the average rate of premature delivery in China is around 10 percent and it is expected to increase by 1 percentage point each year based on trends in recent years," says Ma. "Rates in Shanghai, Beijing and Guangzhou are above 10 percent."

Major factors contributing to premature births include high blood pressure, diabetes, genital tract infections, multiple births and pregnancies among older women (over 35 years), according to Dr Ying Hao, deputy chief of Obstetrics Department at Shanghai No. 1 Maternity and Child Health Hospital.

Drinking alcohol, smoking, inhaling second-hand smoke, working long hours, fatigue, stress, mood swings, lack of exercise and poor eating habits also increase risk. These are frequently part of big city living.

High-calorie, high-cholesterol and fatty foods contribute over time to high blood pressure and diabetes.

Even if diabetic women maintain good health during pregnancy, caesarean sections are usually recommended since the condition is aggravated in late pregnancy.

In addition, age is a factor in premature births when mothers are over 35 or under 20. Both the number of older mothers and young mothers are increasing. Improper induced abortions can cause reproductive system infections that can cause early uterine contractions.

Multiple births, common in vitro fertilization, carry a higher risk of premature births, according to Dr Qin Yan, associate chief physician of the Newborn Department of Shanghai No. 1 Maternity and Child Health Hospital.

A single baby is usually delivered naturally after 39 weeks of pregnancy, twins within 36 weeks and 33 weeks for triplets, says Dr Qin.

"Of course, we cannot control the natural rate of premature delivery, but we can reduce unnecessary risk by knowing the factors that may lead to premature delivery and take preventive measures," says Ma from the Premature Baby Aid Fund.