The great minds at Slate tackle the brainteaser that is how the fuck Nicole Richie, whose body mass index is apparently a "prepubescent" 16, got knocked up. According to the story, the very lowest a woman's body mass index can fall without losing all the gross bodily functions that make us women is 17, and it should really be more like 24 if you're trying to have kids.
Women need fat to signal the pituitary gland to ovulate—without it, their bodies go into a kind of famine mode and won't use up energy to maintain reproductive processes.
According to Wikipedia, which we trust when we're being lazy:
The North Korean government seems to perceive its population as too small in relation to that of South Korea. In its public pronouncements...The state provides t'agaso (nurseries) in order to lessen the burden of childrearing for parents and offers a seventy-seven-day paid leave after childbirth.
Nicole Richie Can Get Pregnant?