While the association between infertility and being significantly overweight is pretty clear, the relationship between being underweight and having trouble getting pregnant is not as clear. There are certain situations in which very thin women do have trouble conceiving, usually because they do not ovulate. Athletes who are training heavily may not ovulate. If they do not ovulate, they cannot get pregnant. Women with anorexia nervosa also do not ovulate normally. However, the answer to the question of whether or not you are too thin to conceive is probably no, as long as you are otherwise healthy, eating a nutritious diet, and exercising moderately.
There is a complex relationship between female hormones and hormones from the pituitary and other parts of the brain. It is relatively easy to disrupt the normal cycle of hormone release. With intense exercise, there is a disturbance in the way the brain releases hormones which can interfere with ovulation and menstruation.
What do you think? Are You Too Thin to Conceive?