The survey from the Pew Research Center says child care costs and student debt are among the factors dissuading potential parents.

In China, each woman went from having about three children in the late 1970s to now one. Decades later, the Chinese government wants women to have three children again but is meeting resistance.

Young, productive workers "are the new scarce resource," one expert says.

As part of our mini-series on fertility, we talk to a demographer about why fertility rates are declining in developing countries.