Having kids is one of those things most of us take for granted — until the day rolls around when we decide we want children and experience trouble conceiving.
Don't miss these Health stories
More women opting for preventive mastectomy - but should they be?
Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.
- Larry Page's damaged vocal cords: Treatment comes with trade-offs
- Report questioning salt guidelines riles heart experts
- CDC: 2012 was deadliest year for West Nile in US
- What stresses moms most? Themselves, survey says
- More women opting for preventive mastectomy - but should they be?
But while some causes of infertility are hereditary or due to health problems beyond your control, reproductive experts say there are a few steps you can take to preserve and enhance your ability to have children.
A healthy lifestyle alone won't necessarily protect you from infertility, cautions Dr. Steven Ory, of IVF Florida Reproductive Associates and an associate clinical professor at the University of Miami.
But it may help.
"The benefits of exercise, a proper diet, maintaining good general health are very important," Ory says. "People who are very unhealthy have a much higher incidence of infertility."
Studying the stats
The prevalence of infertility in the United States today may be as high as one in six couples of childbearing age.
Dr. Samuel Pang, medical director of the Reproductive Science Center of New England, estimates that about one-third of his patients' difficulties is due to a woman's health problem and another third is due to a problem with a man's sperm.
The other third consists of couples whose age is affecting their ability to conceive, a group that's growing as more people delay having children until later in life. Doctors say maternal age in particular is one of the most important factors couples need to consider.
"Sociologically we've changed, but our biology hasn't changed very much," says Dr. Richard Scott, director of Reproductive Medicine Associates of New Jersey. "Women make a lifetime supply of eggs when they're in the fetus. When they're gone, they're gone."
In fact, a woman's fertility starts to measurably decline around age 27, due to the depletion and aging of her eggs. For those under 30, it's estimated that the chance of getting pregnant in any one cycle is 20 percent to 30 percent. By age 40, it falls to 5 percent, according to the American Fertility Association.
Guys, listen up
But it's not just women who need to pay attention to the ticking of the clock, says Dr. Harry Fisch, director of the Male Reproductive Center at New York-Presbyterian Hospital/Columbia University Medical Center and author of "The Male Biological Clock."
Men over 35 are twice as likely to be infertile as those under 25. Studies also are showing that, as with older women, older men are more likely to have children with birth defects due to the decreased genetic quality of their sperm.
"Every cell in the body ages," Fisch says. "Why would you think the sperm or testicles don't age?"
Beyond the age at which we choose to have children, there are other lifestyle factors within our control that can affect a man's and woman's fertility.
"Lifestyle is important for everything, of course it's important to our fertility," says Pamela Madsen, founder and executive director of the American Fertility Association, a national nonprofit organization that raises awareness about the issue.
First off, doctors recommend quitting smoking and, if you're obese or have a BMI of 30 or more, losing weight.
Smoking can increase the risk of a miscarriage and cause a woman's eggs to deteriorate more rapidly — damage that can't be reversed, Ory says. The habit can significantly lower a man's sperm count, too.
Obesity creates hormonal imbalances, preventing women from ovulating normally and affecting men's sperm production, Pang says. Research just published in the European journal Human Reproduction also has shown that when both partners in a couple are overweight or obese, they're more likely to have to wait longer before successfully conceiving a child.
"Losing weight is good for many reasons," says Cecilia Ramlau-Hansen, a visiting scholar at the University of California Los Angeles School of Public Health who led the study. "This is just another."
If you're trying to conceive, a recent University of California San Francisco study shows it might be worth it for men to stay away from hot baths and hot tubs. The findings showed that weekly exposure to wet heat for 30 minutes or more for at least three months could impair sperm production and movement, says Dr. Paul Turek, lead investigator and professor of urology at UCSF.
Doctors also say you shouldn't overlook the possibility that a prescription drug you're taking could play a role. Medications, such as one class of high blood pressure drugs, can be potentially toxic to sperm, Pang says. Antidepressants also may cause irregular menstrual cycles.
And pay attention to what you eat. A new study by Dr. Jorge Chavarro, a research fellow in the department of nutrition at the Harvard School of Public Health, has shown that drinking whole fat milk and eating ice cream may be better for women trying to get pregnant than low-fat dairy products. Chavarro says more research needs to be done in the area and that this kind of step should be temporary, not a permanent lifestyle change. (You should also try to cut calories or saturated fat elsewhere in your diet.)
Most doctors say when it comes to your daily diet your best bet is to use common sense and get plenty of fruits and vegetables . It can't hurt and it should help your body function at its best, something you'll want during the conception process and eventually need to keep up with your baby.
"If you're running a marathon, you've got to train for it," Fisch says, "and if you want to have a baby, you've got to train for that, too."
© 2012 Forbes.com