(HealthNewsDigest.com) - Father's Day is a wonderful time to celebrate the dads of the world, but it's also a good time to talk about men who are trying to become dads.

Some men have fertility issues making it difficult for them and their partner to get pregnant; in fact, male infertility accounts for an estimated 40% of fertility problems in couples who have difficulty conceiving.

When it comes to a man’s fertility, a number of common factors can be at play, says UCLA urologist Dr. Jesse Mills. Here’s what dads-to-be – and their partners – need to know.

Basic lifestyle changes are fundamental

"Eat, move, sleep." That's a mantra Mills, who serves as the director at The Men's Clinic at UCLA, recites to all his patients.

Taking care of diet, exercise, and sleep is a vital part of a man's overall health and, in turn, reproductive health.

• Diet. Focus on fresh fruits and vegetables, high protein foods, and foods rich in polyunsaturated fats (like tree nuts, almonds, and walnuts).
• Exercise. Men should break a sweat for 30 minutes or more each day. "Exercising just once or twice a week is not enough," Mills says. "Anything that improves blood flow, heart rate, and metabolism is probably going to translate to better sperm production."
• Sleep. Try to get more than six hours of sleep per night. "When men sleep, they recharge their pituitary gland, and the pituitary gland controls sperm production by the testicles," Mills says. "If you're consistently not getting enough sleep, there's a good chance the hormones that control sperm production are lagging."

Overweight or obese men have a higher incidence of fertility issues. One potential reason is that larger thighs can cause the testicles to be at a higher temperature, affecting sperm health. Obesity also causes decreased testosterone.

In any event, diet, exercise, and sleep all help to stabilize weight – and improve a man's health overall.

Stress is a very real factor in fertility

"I can't tell you how many men I see in my clinic that are not only stressed professionally but have the added stressor that comes with trying to get pregnant," says Mills. "Just that stress of making a baby is enough to send couples fighting and not being able to accomplish their fertility goals, and that doesn't do anyone any good."

If stress is an issue, it's important to do what you can to reduce it. Again, exercise helps, says Mills, as does sufficient sleep.

Some things can signify a potential medical problem

There are certain red flags that could indicate a potential medical problem affecting a man's fertility. Mills says men should look out for the following issues and let a physician know if they're experiencing any of them:

• Pain during ejaculation. Men should not be experiencing pain during ejaculation. It could indicate an infection or a blockage such as an ejaculatory duct stone, a calcification similar to a kidney stone but located somewhere along the reproductive tract.
• Low ejaculate volume or irregular ejaculate color. Normal ejaculate volume should be about half a teaspoon to a teaspoon. Ejaculate should ideally be a pearly white color.
• Abnormal testicle size or feel. A healthy man's testicles should feel firm and should be close to the size of an apricot. Softness or squishiness usually indicates a problem with sperm production, as 80% of the size of the testis is devoted to sperm production.

If any of the above medical issues pertain to you, or if you and your partner have been trying to conceive for six months without a pregnancy, a visit to a men's health specialist is a good idea. Physicians are able to perform a number of tests to determine the root of fertility issues, and there are a number of surgical and medical options to repair such issues and help couples reach their fertility goals.