In late 2015, when China eased its decades-long policy limiting most couples to having only one child, some heralded the change as a move toward greater reproductive freedom. But the government was only embarking on another grand experiment in population engineering: This time it was urging women — though only the right sort — to reproduce for China.

The authorities in Beijing seemed terrified that plummeting birthrates, an aging population and a shrinking labor force might undermine the results of years of double-digit growth rates, and threaten the political legitimacy of the ruling Chinese Communist Party (C.C.P.). So they began allowing most married couples to have two children. They hoped that the new policy would bring three million additional births a year through 2020 and add more than 30 million workers to the labor force by 2050.

But there has been no baby boom. Figures released last month show that the country’s birthrate fell by 3.5 percent in 2017 compared with the previous year. (The number of births had increased in 2016, the first year since the policy shift, though far less than the government had hoped.) According to official statistics, the number of children born to parents who already had one child did rise in 2017, but the number of first-child births dropped.

Why? Because a critical mass of women appears to be in no rush to have babies, particularly urban, educated women — just the category that the C.C.P. is counting on to produce and raise a new generation of skilled, knowledge-based workers.