So what is causing this plunge? Gavin Jones, a demographer based at the National University of Singapore, identifies primarily rapid urbanization and sky-rocketing house prices. In 1979, China’s population was 80 percent rural; today the proportion is roughly half that.

This transformation makes reversing the one-child policy largely moot, Jones says. Indeed a 2013 easing of restrictions on family size in certain circumstances elicited far fewer takers than expected. Barely 12 percent of eligible families even applied.

One critical problem is the high cost of real estate, particularly in China’s most important cities, which makes it difficult for young couples to attain the space to house a larger family, let alone leave them sufficient financial resources to raise the children. China’s main cities have suffered arguably the world’s most rapid growth of property prices relative to income. Last year, The Economistestimated house price to income ratios of nearly 20 in Shenzhen 17 in Hong Kong and over 15 in Beijing, between 50% and 100% higher than ultra-expensive Western places like San Francisco, Vancouver or Sydney.

This explains in part why prosperous cities like Shanghai and Beijing, now have among the lowest fertility rates ever recorded — down near 0.7 per woman, or one-third the replacement rate. If the experience of densification and high prices spread to other Chinese cities, officials may be lucky if couples even bother to have one child.