Diabetes affects male fertility as well. Diabetic men often experience retrograde ejaculation in which semen enters the bladder instead of being ejaculated through the penis into the female reproductive tract where it can fertilize eggs. Diabetes also can cause erectile dysfunction.

High blood pressure. "The relationship between chronic hypertension and infertility isn't clear," notes Kaylen M. Silverberg, MD, medical director of the Texas Fertility Center in Austin and obstetrics and gynecology professor at the University of Texas Medical Branch in Galveston and the University of Texas Health Science Center at San Antonio. Chronic hypertension does, however, appear to contribute to infertility in certain people (one reason may be the conception-thwarting impact of high blood pressure drugs).

Having uncontrolled high blood pressure while you're pregnant -- either because it wasn't under control before conception or because it develops afterward (a condition known as preeclampsia) -- can invite serious complications, including constriction of blood vessels in the uterus that cuts off oxygen and nutrients to your baby; separation of the placenta from the uterine wall, which may lead to heavy bleeding and shock; and eclampsia, a life-threatening complication of preeclampsia, which may include convulsions and coma.

Thyroid disease. Having an underactive thyroid gland (hypothyroidism) or an overactive one (hyperthyroidism) can scramble your ovulation cycles and short-circuit your ability to conceive. Hypothyroidism may also be associated with an autoimmune response in your body, signaling it to manufacture antibodies that attack your ovaries and lead to premature menopause.