Can weight loss increase fertility?

On the previous page, we brought up the connection between obesity and infertility. That's because there's a growing mountain of evidence linking the two.

For example, research shows that spontaneous pregnancy (pregnancy without fertility treatments) becomes less likely the higher a woman's body mass index (BMI) is more than 29 [source: Science Daily]. In particular, severely obese women are 43 percent less likely to get pregnant than women who are of average weight or simply overweight (but not obese) [source: Boyles].

And it's not just women whose fertility is influenced by weight. Men, too, can experience reproductive challenges due to obesity. A Danish study found that men with a BMI over 25 had around 22 percent lower sperm concentration and 24 percent lower sperm count than men of normal weight [source: WebMD].

Interestingly, the study examining female fertility noticed problems primarily in obese women (BMI over 30); whereas the study observing male fertility sees trouble starting when the BMI is around 25, which is considered overweight but not yet obese.

While such results may be confusing, the best lesson to be taken from them is -- overweight or obese -- both partners should consider losing weight, if necessary, to increase the odds of conception.

To learn more about how weight affects fertility, head to the next section.

We've pointed out that obesity can hinder your odds of getting pregnant. But you might be wondering how exactly preconception weight affects your fertility. Medical scientists, too, are still trying to find specific answers to this question. The issue is complex and still being actively investigated by researchers, but experts do have insight into a couple of ways obesity impacts fertility:

Of course, these are ways in which obesity effects fertility. But did you know that being underweight can also have a major impact on your ability to get pregnant? We'll look at that particular problem on the next page.

Celebrity news reporter Giuliana Rancic famously publicized her infertility struggles on her reality TV show. And in an interview with Barbara Walters, she admitted that her doctor told her to gain weight to improve her chances of becoming pregnant [source: Glines].

As it so happens, very thin women like Rancic tend to have more trouble conceiving than obese women do. A recent study examined three groups of women seeking in vitro fertilization (IVF) procedures: very thin, normal weight and obese. The normal-weight women had a 50 percent success rate with IVF, obese women had 45 percent and thin women had only 34 percent [source: Macrae].

Low bodyweight can also prevent a woman from conceiving naturally. One possible reason for this is that being underweight can lead to amenorrhea, the absence of menstrual periods [source: Mayo Clinic]. If you're experiencing amenorrhea, you're not ovulating. Thin women may also have irregular periods, which can lead to inconsistent ovulation.

A man who's too thin can be infertile as well. Just as being overweight can reduce a man's sperm count, so can being underweight [source: Levine].

So don't think you're off scot-free just because you're not overweight or obese. If you're having a difficult time conceiving and either you or your partner has a body mass index (BMI) under 18.5, you should consider a healthy weight-gain regimen recommended by a dietitian or physical trainer.

For more tips on improving your fertility, click on the next page.

So, by this point you know two important steps to improving your fertility: If you're obese, lose weight; if you're underweight, gain it. But, obviously, that's not all. If weight were the only factor influencing a couple's ability to conceive, the world would have fewer fertility clinics and lots more babies.

Fortunately, there are other things you can do to increase your chances of getting pregnant. In addition to weight management, both men and women should:

In addition,women should avoid vigorous physical activity when trying to get pregnant. Going overboard with exercise can reduce progesterone production and interfere with ovulation [source: Mayo Clinic]. To a lesser degree, excessive exercise can impact a man's fertility by reducing testosterone levels [source: Levine]. Of course, moderate physical exercise is allowed for both sexes -- even recommended.

While men should follow the same general guidelines as women, there are a few differences to keep in mind. For example, abstaining from sex for more than a few days can affect a man's sperm quality. And certain male-specific health conditions, like low testosterone and variococeles (varicose veins in the testicles), should be addressed by a doctor so that they don't interfere with conception. As for the boxers vs. briefs debate: There's no scientific answer to that question, but educated guesses land on the side of boxers [source: Levine].

If you'd like to learn more about fertility, check out the resources in our next section.