China introduced its so-called one-child policy more than three decades ago as a control mechanism when rapid population growth was outstripping growth in the country's food supply.

Married couples in cities were limited to just one child as part of the government's family planning programme implemented in 1979, when the birth rate was three children per woman.

By 2008 the birth rate had dropped to 1.8 children per woman.

The government says over 400 million births have been prevented as a result of the policy without it, the population today would have been 1.7 billion people, instead of 1.3 billion.

But the city of Yicheng has challenged this claim.

Chinese authorities selected Yicheng 30 years ago for a secret experiment: to act as a control group to see what would happen if families had the freedom to have more than one child.

And the population there has actually grown at a slower rate than the national average, as Al Jazeera's Melissa Chan reports.