Many women feel they have to choose between their children and their careers. Women who prosper in high-pressure companies during their 20s drop out in dramatic numbers in their 30s and then find it almost impossible to regain their earlier momentum. Less-skilled women are trapped in poorly paid jobs with hand-to-mouth child-care arrangements. Motherhood, not sexism, is the issue: in America, childless women earn almost as much as men, but mothers earn significantly less. And those mothers’ relative poverty also disadvantages their children.