Kanazawa doesn't give a reason why this is a case, The Guardian reported, and it's not clear why some of these "loser" women elect to do something as "unnatural" as not having children. However, it is becoming more common, at least in the United States. According to a Pew Research report from 2010, one in five American women did not have children when her biological clock stopped ticking, compared to one in 10 in the 1970s, Time reported.