As rumors swirl around NBA player Tristan Thompson cheating on new mom Khloé Kardashian during her pregnancy, let's get real about the signs of infidelity and how to keep intimacy in your relationship during this transitional time.

Gretchen was six months pregnant when she found out that Marcus, her live-in partner of nearly 10 years, had been having an affair. Devastated, she confronted him, and he confessed. Today, more than a year after her discovery, she is raising their toddler daughter alone and has still not told her family the real reason she and Marcus parted.

Pregnancy can lead to greater intimacy, but it also can trigger less pleasant changes in a relationship, including infidelity. Estimates of the number of men who stray during their partner’s pregnancy are understandably difficult to gauge, because it’s a topic no one wants to discuss. “You’re not likely to hear about it, especially during the pregnancy, but it’s probably more common than people suspect,” said Scott Haltzman, M.D., a clinical assistant professor of psychiatry at Brown University Medical School in Providence, R.I., and author of 2008’s The Secrets of Happily Married Women.

Perhaps surprisingly, the cheating isn’t necessarily about the need for sex itself. “It can also stem from an emotional need, like a desire to be cared for, to feel important or special,” Dr. Haltzman explained. Given all the changes that occur during pregnancy, such needs that might otherwise be satisfied by a man’s partner often go unmet. “For many men, engaging in sex is a form of emotional closeness,” Dr. Haltzman says. “When their partners push them away, they feel rejected not just sexually, but also emotionally.” Many men also fear the situation will get even worse after the baby is born.

Such was the case with Troy, who had an affair during his wife’s third pregnancy. “There was such a focus on her, with all she was going through and about to go through, that I became less and less relevant,” he recalled. At the same time, his wife began rejecting his sexual advances. Although he understood she was feeling insecure about her changing body, the rejection was still difficult to manage. “You only need to be turned away so many times before you get the picture,” he said. Troy’s wife never found out about his infidelity and they remain married today, although he has no regrets.

“I wanted to feel important and valued,” he said. “And it worked.” This doesn’t mean dads-to-be get a free pass for bad behavior. They should realize that a woman undergoes tremendous physical and emotional changes during pregnancy. A little understanding—on both sides—can go a long way.

Recognize the signs

While infidelity during pregnancy may be more common than we think, you shouldn't necessarily go looking for signs of infidelity. "Be alert in the same way you are alert to giving yourself a breast exam every month,” Dr. Houston said.

Ruth Houston, the founder of InfidelityAdvice.com and author of 2002’s Is He Cheating on You?–829 Telltale Signs, advises expectant moms to be mindful of the relationship challenges that pregnancy can pose. “It’s very important for women to be aware that this is a critical time and to be vigilant,” she advises, adding that potential clues include unexplained absences, strange phone calls, spending more time “at work,” less interest in sex and a greater focus on his appearance.

You have to be aware that hormones may be affecting your thoughts and emotions, Dr. Haltzman cautioned. Rather than jumping to conclusions alone, process your feelings with a trusted confidante outside the family. If a certain behavior seems suspect, ask questions rather than accuse when broaching the subject. “Your first approach may be to ask your partner if he can explain [the behavior in question],” Dr. Haltzman recommended. But because deceit is one of the hallmarks of infidelity, direct accusations will often be met with denial.

According to Dr. Haltzman, the only way to get confirmation may be to do a bit of investigating. Gretchen caught Marcus after reading incriminating text messages on his cellphone. If infidelity is confirmed, it’s time to seek assistance from an outsider. “You need to get a third party, like a therapist, involved to help you sort out what, if anything, is going on,” Dr. Haltzman said.

An ounce of prevention

Despite the challenges pregnancy brings to a relationship, infidelity is not inevitable. One thing you can do is sit down with your partner as early as possible in the pregnancy to discuss what your plans might be if your sexual interest drops. “If you say, ‘I really want to talk about our options if I don’t feel like having sex,’ believe me, he’s going to pay attention,” Dr. Haltzman said. And sex doesn’t have to involve intercourse. “Experiencing sexual release through touch, mouth, or massage speaks very powerfully to men,” he explains.