The male and female reproductive systems are engineering marvels. To function optimally, both rely on an equisite balance of precisely timed hormonal messages and the peak performance of the reproductive organs. Unfortunately, a chronic health condition such as diabetes or thyroid disease can sometimes snarl these intricate reproductive works. Aggressively treating conception-threatening conditions before you're ready for a baby is your best insurance against infertility. Here's a list of the chronic conditions you need to get under control now.

Diabetes. Type 2 diabetes (also called adult-onset diabetes) is linked to obesity and insulin resistance, both of which can cause hormonal upsets in women, out-of-whack menstrual cycles, and infertility.

Type 1 diabetes (sometimes called juvenile-onset or insulin-dependent diabetes) develops when the insulin-producing cells of the pancreas are destroyed by autoantibodies. This process may cause the body to make antibodies that attack other endocrine organs, including the ovaries. The result may be a depletion of eggs and early menopause.

Blood sugar is difficult to control with type 1 diabetes because all of the insulin the body needs must be given by injection. If you do conceive, diabetes can seriously harm your baby if you haven't yet reined in high blood sugar. Women with poorly monitored preexisting diabetes in the early weeks of pregnancy are two to four times more likely to have a baby with birth defects, incudling neural tube defects like spina bifida. They're also at greater risk of miscarriage, stillbirth, or high-birth-weight babies that are difficult to deliver. If you develop gestational diabetes later in pregnancy, you boost your odds of having a larger than normal baby or one with birth defects.