In the US 25% of mothers are back at work within 2 weeks of childbirth (https://www.vox.com/2015/8/21/9188343/maternity-leave-united...). FMLA requires jobs to let mothers take time but does not require they be paid, and most folks are living paycheck to paycheck and need the money.
It's a Department of Labor study, so presumably done on people already in the labor force. Doesn't change how terrible the stat is, even assuming 50% of mothers aren't in the labor pool that'd still be 12% of mothers back in work in under two weeks.