The number of children of illiterate women at childbearing age in this city is five times higher than that of women with master's degrees, according to a recent survey by Shanghai statistics bureau.

Based on the data collected as part of the sixth national census conducted in 2010, the survey found that a woman with a higher educational background was more likely to have less children. In 2010, a woman of childbearing age (defined as those between 15 to 50 years old) in Shanghai had 0.8 children on an average.

Women with master's degrees had an average of 0.36 children, as against the 1.8 averaged by women who never went to school.

"It is common not only in China but also across the world that women, the more highly-educated they are, tend to have fewer children," said Xu Anqi, director of the Shanghai Academy of Social Sciences' family study center.

In addition to economic consideration, psychological factors such as job-related stress and physiological ones, like the time taken for postpartum recovery, make many highly-educated women hesitate about having a child, according to Xu.

She also mentioned that in countries like China where while women's career opportunities have expanded and yet they were expected to do most of the housework and look after the children, many women were opting out of having children, as they felt it would be difficult to balance their professional and familial roles.

Miao Yanjie, a 27-year-old fashion designer who got her master's degree in Italy, never told her boss and colleagues at a Shanghai-based clothing firm that she got married on Nov 25.

"If I let them know I'm married, it might affect my prospects, getting pregnant even more so," she said. "I plan to have a baby at 29 or 30 - after securing a higher position in my company."

Miao said one child would be more than enough for her newly-established family. "A can of imported milk powder costs about 1,200 yuan ($188) and you want to give your child only the best things available," Miao said.

The fact that the average age of Shanghai residents is getting higher has also contributed to this phenomenon.

"Young couples having to leave their children with their aging parents is a growing trend," said Xu.

"Those with high education tend to get married late and delay the arrival of children. By the time they have children, 60-something grandparents are often lacking the energy to look after two children or more," she said.

Yin Ping, a Shanghai mother with two children, however, said she observed an increase of "second child boom" in recent years. The 30-something master's degree holder quit her job and paid up the 180,000 yuan fine to have a second child three years ago.

"More and more of my friends from a similar background as mine are having a second child or considering having one."

The survey also showed that the number of Shanghai-based women in their childbearing age decreased by 12.68 percent in 10 years' time. The city's population of immigrant fertile women, however, increased by 67.42 percent.

"The growing migrant population is the main cause for the increasing number of babies," said Xie Lingli, director of the Shanghai Population and Family Planning Commission.