Men also should moderate their alcohol intake. "If they drink more than two drinks a day, they may make fewer sperm or make what I call 'sloppy swimmers,'" says Dr. Mazzullo. "The sperm is developed, but it doesn't get the job done."

Likewise, men and women trying to conceive should reduce their caffeine intake to fewer than two caffeinated beverages a day to avoid impairing sperm motility and female fertility.

Smoking or using illegal drugs can have serious effects on the developing fetus. Smoking and other forms of tobacco use can lead to an infant who is underweight or with hindered intellectual or emotional development. Illegal drugs can cause birth defects, developmental disorders and respiratory problems. Children whose mothers used illegal drugs during pregnancy may be addicted to the drugs.

Get in the exercise habit

Women who exercise before pregnancy tend to be healthier during pregnancy.

"By preparing your body ahead of time, you're getting it in the best possible shape for the marathon of pregnancy," says Dr. Mazzullo.

Although exercise, per se, doesn't affect a man's fertility, what he wears during exercise can. Men who spend time a lot of time in a jock strap, for example, should limit wearing one as much as possible during the conception period because it can heat the testicles and lower sperm count. For the same reason, men also should limit their time in a hot tub, spa or steam room to 15 minutes twice a week.