The U.S. is the only developed nation still debating whether a woman should have access to paid maternity leave. More often than not, the answer to that question lies with the employer's policies; there is no federal program that covers all women in America. Outside America, the question isn’t whether paid leave is an option, but how much of it she can and should take.

The answer varies. The United Nations agency International Labour Organization recommends at least 14 weeks of paid leave. But many countries go far beyond this. For instance, the United Kingdom mandates that women receive 90 percent of their average weekly earnings for up to nine months after giving birth, and Swedish women get up to 16 months of paid leave. In many European nations, paid leave policies range anywhere from four months paid time off to over a year. The amount of protected leave, or the time a parent can care for a child without fear of losing her job, can extend even further—up to three years in places like Finland and Spain.

But how much is too much? There’s a catch to generous paid leave: When these policies are badly executed, they can reinforce the glass ceiling.

First, it's important to acknowledge that the absence of universal paid leave represents a tremendous disadvantage for working women in America. Without paid leave, women are more likely to exit the workforce. If and when they reenter, they may return to lower-paying jobs, or no job at all. Many believe that the overall lower participation of women in the workforce is a result of the lack of paid leave: Economists estimate that women’s labor force participation is lower for 25-54 year-olds than it would be in America if there were universal paid leave. The effects seem to be growing more serious: A comparative study of 22 countries found that the U.S. fell from the sixth-highest in labor force participation for women in 1990 to 17th by 2010. The Cornell economists, Francine Blau and Laurence Kahn, found that the lack of paid leave explained about one-third of this decline.

But even with paid leave, there are tradeoffs when women leave the workforce, especially for long-term leave of a year or more. Blau and Kahn write “it is plausible that the generous parental leave mandates ... reduce the likelihood that women will be able to enter high-level jobs, which generally require full-time, full-year, career-long commitments.” Long leave may allow women to extend their time away from work, but this may lead to some implicit discrimination on the part of the employer: “such policies may lead employers to engage in statistical discrimination against women for jobs leading to higher-level positions, if employers cannot tell which women are likely to avail themselves of these options and which are not,” they write.