Sex ratio grows

The rise in the migrant population in Shanghai has also contributed to the city's birth peak in recent years, according to Huang Hong, the commission's director.

By 2012, there were 23.8 million residents in the city, about 330,000 more than the previous year. Migrants who have lived in the city for more than six months are counted as residents.

There were 9.6 million migrants in 2012, about 250,000 more than in the previous year. They account for about 40 percent of the city's total population.

Last year, 105,000 babies were born to the migrant population, up by 33.8 percent from 2011.

"The steady rise in the city's population in recent years is partly due to the increasing migrant population and more births," Huang said.

The population density is increasing rapidly in the city's suburban areas and outskirts, where the migrant population is mainly concentrated. The city is taking efforts to have a balanced population distribution.

Huang said the increasing migrant population has not only brought more births to the city but also widened the gap in the city's sex ratio because many migrants who come from rural areas traditionally favor boys than girls.

Shanghai's sex ratio was 112.4 boys to 100 girls in 2012, a drop of 0.7 from the previous year. The ratio for the city's registered population was 103-107 boys to 100 girls, while the ratio among the migrant population was 117.8 to 100, according to the commission.

The commission has announced that the city will carry out a pilot project for the registration of hospital births and set up stations to monitor the sex ratio.

Under the pilot project, the use of identity cards will be required when registering newborn children. It aims to create a more accurate picture of newborns in the city.

Authorities said they will strictly monitor the sex ratio and crack down on illegal clinics that notify parents of the sex of the unborn and carry out abortions.

In addition, people who provide tips about illegal births will be rewarded by the government.