Is being underweight associated with infertility?

Yes: Our findings over the last few years point to an enormous increase in ovulation problems for underweight women. It's complicated but even with regular cycles, infertility or miscarriage can be the result. In today's high carbohydrate nutrition world, the only way to stay underweight is to intermittently starve or be low on calories creating a stress induced ovulation problem. There's more.....

If irregular cycles: Low body weight may be associated with lower fertility, especially if you also have irregular periods / no cycles. This means that you're not ovulating (releasing an egg) every month. This can be due to low levels of hormones that control your cycles from the pituitary gland, known as hypogonadotropic hypogonadism, which is more common with underweight, stress, eating disorders, or heavy exercise.

Yes: being significantly underweight can cause amenorrhea (lack of periods) which causes infertility. See your doctor about gaining weight in a safe manner. If your being underweight is due to anorexia or some other eating disorder, seek a counselor for proper treatment. Hope this helps!