We don't see a lot of images of fertility goddesses as skinny stick figures. And it's true that underweight women make a form of estrogen that can be too weak for successful conception, according to the American Society for Reproductive Medicine
(ASRM). While obese women often have an overabundance of estrogen, this can affect their cycle to the point that they stop ovulating. Excess weight can influence fertility in other ways, too: A 2007 Dutch study of more than 3,000 couples (without any known ovulation problems) found that women with a body mass index of 30 or higher had significantly lower probability of becoming pregnant naturally
, when compared with women with BMIs of between 21 and 29. This is why the ASRM stresses the importance of maintaining a healthy weight for those trying to conceive. By the way, having full hips won't even provide an advantage during childbirth; "It's the front-to-back dimension that creates the tightest squeeze," discovered Nathanael Johnson
while exploring the science and history of childbirth (among other biological processes) for his book All Natural
. So a tall, average-weight woman has the best chance of getting pregnant naturally and giving birth more easily.