It takes two to make a baby. Although a woman will carry and deliver the child, a man also has a leading role in pregnancy. For fertilization to occur, his sperm must be healthy and strong to reach and penetrate her egg. 

To make this process happen, a man must be able to have and keep an erection, have enough sperm that are the right shape and move in the right way, and have enough semen to carry the sperm to the egg, suggests the U.S. Office on Women’s Health (OWH). A problem in any step in this process can cause trouble conceiving. 

A variety of factors, from genetics and lifestyle to environmental exposures and hormones, can affect a man's fertility, so it's difficult to isolate the exact cause for infertility, said Dr. Jared Robins, chief of reproductive endocrinology and infertility at Northwestern Medicine's Fertility and Reproductive Medicine in Chicago. 

In fact, doctors can identify the cause of problems in about 80 percent of infertile couples, Robins noted. When there is a known cause of infertility, problems in the male partner tend to account for about 40 percent of infertile couples, Robins said. 

When asked for his most important recommendation for men who want to start a family, Robins said, "A man should make sure he has a happy, healthy lifestyle — and a good relationship." 

Robins said one of the problems he sees is that when couples become so fertility focused, they essentially stop having sex until they think it's the best times to conceive. "Their sex lives become focused on pregnancy, so infrequent sex can be a problem in these couples," he said. 

The focus on fertility can also be stressful on a relationship, Robins noted. But there are many steps that men can take to enhance their health, lifestyle and relationship to increase a couple's chances of conceiving. 

Here are 12 tips for men who want to improve their fertility.

1. Lose extra pounds.
Studies have suggested that couples in which the man is overweight or obese and the woman is of normal weight take longer to conceive than couples with no weight problems. 

Some research has also shown that being overweight or obese affects a man's sperm quality, reducing sperm counts and decreasing their ability to swim, as well as increasing damage to genetic material (DNA) in sperm, according to the American Society for Reproductive Medicine. 

A recent study found that overweight and obese men were more likely to have low sperm counts or a lack of viable sperm compared with normal-weight men, possibly making it harder for these men to father a child. The researchers suspect that too much body fat may be linked with changes in testosterone and other reproductive hormone levels in men.

2. Get health conditions under control.
Effectively managing chronic medical conditions, such as high blood pressure and diabetes, may improve a man's chances of getting his partner pregnant, suggests The American Society for Reproductive Medicine. Other medical conditions, such as cystic fibrosis or varicoceles (enlarged veins in the scrotum that cause overheating), may also affect male fertility, according to the Centers for Disease Control and Prevention. 

In addition, some medications used to treat high blood pressure (beta blockers), depression and anxiety (SSRIs), pain (long-term opiates), and an enlarged prostate (finasteride), could have a negative influence on fertility. Supplemental testosterone can also decrease sperm production. 

Some chemotherapy drugs and radiation treatments for cancer can cause permanent infertility, according to the Mayo Clinic. 

A man should speak to his doctor if the medication he is taking might interfere with his ability to father a child.

3. Eat healthy foods.
"The role of diet in male fertility is unclear," Robins told Live Science. 

Even though the science may be inconclusive, it still makes sense for men to eat a variety of healthy foods, including plenty of fruits and vegetables, which are rich sources of antioxidants that may help to produce healthy sperm. Men should also consume fiber-rich foods, healthy monounsaturated fats, and moderate amounts of lean protein. 

Robins said men frequently ask him whether drinking soda can decrease their sperm counts. He tells them there's no good evidence that caffeine in soda affects men's fertility, and there's little evidence that caffeine in coffee, tea and energy drinks is linked with fertility problems in men.

4. Get regular physical activity.
Robins said he encourages men to get regular exercise because it helps reduce stress, makes men feel better about themselves and benefits their long-term health. 

While being physically active is beneficial, some studies have suggested that overly intense exercising and a strenuous training schedule in men, such as triathletes and marathon runners, may be detrimental to their fertility. 

Researchers have also looked at whether bike riding can affect sperm because the sport involves long periods of sitting in a position that increases scrotal temperatures as well as bouncing and vibrations that could cause trauma to the testicles. (A few studies have suggested that long-distance truck drivers may also have more fertility problems for similar reasons as avid male cyclists.) 

One study found that men who attended fertility clinics and who reported they cycled for at least five hours a week were more likely to have low sperm counts and poor sperm motility compared to men who did other forms of exercise and those who were couch potatoes. 

Other research has suggested that bike riding in men is linked with a higher risk for erectile dysfunction. But there's little data on whether or not cycling actually impacts sperm function, Robins said.

5. Take a daily multivitamin.
Robins tends to recommend that men take a daily multivitamin. "There is little likelihood of harm and some potential benefits," he said. 

Many multivitamin formulations for men might include antioxidants, such as vitamins C and E, and the minerals selenium and zinc. Some research has found that antioxidants may cause a slight increase in sperm count and movement, according to The American Society for Reproductive Medicine. 

It makes sense that antioxidants may improve sperm quality because they can protect against free radicals, which can cause damage to DNA within sperm cells, Robins said.

6. Be conscious of age-related fertility changes.
Men also have a ticking biological clock, but they experience fertility declines later in life than women do. Research shows that as a man gets older, both the volume and quality of his semen tends to diminish. 

In men over 50, there is a decline in testosterone levels, which can impact sperm function, Robins said. As men get older, there is also a falloff in the number of healthy sperm and their movement, and they can also have more DNA damage in their sperm. These changes could mean it might take longer for a couple to have a baby. 

As men get older, there is also a greater risk for genetic abnormalities in their sperm. Random mutations in a man's sperm can pile up as the years go by, making older fathers more likely to pass on more genetic mutations to a child. 

Research has found that older men are more likely than younger men to father a child born with autism, schizophrenia and Down syndrome.

7. Ditch the butts.
Smoking is linked with reduced sperm quality: Research has shown that male smokers are more likely to have low sperm counts and decreased sperm movement, and they have higher numbers of abnormally-shaped sperm, according to the American Society for Reproductive Medicine. 

Smoking might also decrease sperm's ability to fertilize a woman's egg. These are all good reasons why wannabe dads should take steps to quit smoking. 

Marijuana and other recreational drug use, including anabolic steroids for bodybuilding, should also be avoided because some studies suggest they may also negatively impact sperm production, Robins said.

8. Ease up on heavy drinking.
Many women will steer clear of alcohol when they want to become pregnant, so men could also use this as an opportunity to cut back on beer, booze and binge drinking, too. 

Research has found that heavy drinking in men can reduce sperm quantity and quality. When a couple is trying to conceive, men should limit alcohol to low or moderate amounts. 

Moderate alcohol consumption in men is considered two drinks or less per day. One drink equals 12 ounces of beer, or 5 ounces of wine, or 1.5 ounces of liquor, according to the Mayo Clinic.

9. Make healthy lifestyle choices.
Environmental exposures may have negative reproductive consequences for men. Exposure at work to certain toxic chemicals, such as those used in dry cleaning and printing, or to pesticides for agricultural workers, and heavy metals in industrial jobs, might be a possible cause of reduced fertility in men, said the American Society for Reproductive Medicine. 

One small study about men using laptops received plenty of media coverage when it reported that men who placed the computers on their laps may be more likely to have damaged sperm and decreased sperm motility. 

But these conclusions were "jumping the gun," Robins said. It's unclear how much time the men spent with the laptop in close proximity to their testicles, he explained, and it's also unclear whether the effects may have been caused by heat or if they resulted from radiation due to the use of a wireless connection. 

A few studies have also suggested that sperm counts may be affected when men regularly keep their cell phones in their front pant's pocket. But Robins said there has been no research linking this finding to a man's inability to father a child.

10. Boxers or briefs?
"This is everyone's favorite question," Robins said, chuckling. 

But there's not a lot of science to suggest that switching from briefs to boxers improves a couple's chances of getting pregnant. 

Although a man's underwear choice may affect his scrotal temperature and reduce sperm quality, most studies have demonstrated no real difference between boxers and briefs in terms of their impact on male fertility, Robins said. 

A 2016 study published in the journal Andrology was one of the more recent studies to investigate whether the type of underwear that men wore — or its absence — affected the time it took for a couple to become pregnant during a 12-month period. 

The study asked about 500 men to describe their underwear choices during the day as well as at night. The researchers found that it really didn't make much difference whether men wore boxers or briefs or went commando on a couple's ability to conceive or on a man's semen quality, suggesting that it's best for men to wear whatever feels most comfortable to them when a couple wants to have a baby.

11. Beware of the heat.
Frequent visits to and long stays in hot tubs, saunas and steam rooms could increase scrotal temperatures, which may decrease sperm counts and sperm quality. 

But this heat exposure does not have a permanent impact on sperm, Robins said. 

Reduced sperm counts may only be temporary and could return to normal in a few months once a man stops going into a hot tub or sauna.

12. Know when to get help.
Infertility is defined as the inability of a sexually active couple who are not using birth control to get pregnant after one year of trying, according to The American Society for Reproductive Medicine. 

Robins said he tells couples that a woman who is under the age of 35 and her partner should try to become pregnant for one year without success before seeking an infertility evaluation. 

For women who are 35 or older, the time before seeing an infertility specialist shortens to 6 months in couples who are having sex regularly without using birth control, he noted.

First published on LiveScience