Plan checkups for both parents-to-be. This is the time to talk about your medical history, ask questions, and find out whether any tests are recommended. This preconception visit is especially important if you have preexisting conditions, such as thyroid disease or diabetes, or if you have had problems with a previous pregnancy. Note that the father's health and habits also play a role in the health of your baby. "Most men don't think they need to do anything," says Dr. Cole. "[But] sperm are the unindicted co-conspirators when it comes to birth defects. Sperm are as affected by tobacco, alcohol, and recreational and prescription drugs as eggs."