Nausea, breast tenderness, fatigue, and the biggie: a skipped period. These symptoms would have a woman in her 20s rushing to the pharmacy to pick up a pregnancy test, or booking an appointment with her gynecologist. For her, they point to one thing: pregnancy.

But that same woman in her 40s might just assume that she’s experiencing the classic signs of perimenopause, the confusing time frame leading up to menopause. It can last anywhere from 12 months to over four years, according to the Cleveland Clinic. And it’s characterized by…nausea, breast tenderness, fatigue, skipped periods, heightened emotions, brain fog. Sound familiar?

It’s not just that middle-aged woman herself who might write off these symptoms as perimenopause, either. Kate White, MD, MPH, a family-planning specialist who is the vice chair of academics in the department of ob-gyn at Boston Medical Center, says she’s had several patients who called their primary-care doctors about such symptoms and were told, “It’s probably menopause,” only to end up in her office a month later to confirm that they were, in fact, pregnant. “They were given bad information,” says Dr. White.

Lorraine Chrisomalis-Valasiades, MD, a gynecologist and obstetrician in New York City, concurs. “I’ve had two 45-year-old patients who discovered they were pregnant in the last six months,” she says. “So it does happen.”

That’s not to say it happens often; the chance of pregnancy definitely drops with age. As the American College of Obstetricians and Gynecologists reports, “for healthy couples in their 20s and early 30s, around 1 in 4 women will get pregnant in any single menstrual cycle. By age 40, around 1 in 10 will get pregnant per menstrual cycle.”

And the odds continue to go down from there. “I would say the average perimenopause typically starts around 45,” says Navya Mysore, MD, a family physician and the national program director of reproductive and sexual health and medical director of One Medical Group. “And the likelihood of getting pregnant at 45 or beyond is no more than 3 or 4 percent.”

You’ll notice, however, that neither of those numbers is zero. Which is why Dr. Mysore found herself in an ER once, attending a 46-year-old woman with stomach pain who turned out to be six months pregnant and explained, “I just thought I went into early menopause, like my mother.”

The moral of the story is: If you’re a woman who is not interested in conceiving and thinks she might be experiencing perimenopause, the key to not ending up in a “Surprise, you’re pregnant!” situation is to be informed, aware, and proactive. Read on for the experts’ answers to all your questions about the intersection between the menopause transition and pregnancy symptoms.

How Do I Know If I’m In Perimenopause?

While menopause is an exact moment—12 months after your last period—perimenopause is the period of time before that when the menstrual cycle often becomes irregular, as your hormone levels drop and your body approaches menopause. “The average age of menopause in the United States is 51.4,” says Dr. Chrisomalis-Valasiades. “You can start getting perimenopausal symptoms as early as 43, 44, 45,”—or even earlier, if you’ve had one or both ovaries removed or are simply predisposed toward early menopause.

Also, however, keep in mind that it’s not over till it’s really over. “The definition of menopause is 12 months in a row with no bleeding—which means if you go four months with no periods and then have one, the clock resets,” says Dr. White. Once you’ve reached menopause—12 months with no period—you’re not going to get pregnant. But in the twilight zone before that known as perimenopause, you still can and might conceive.

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What Symptoms Are Common To Both Pregnancy And Perimenopause—And What Should I Do If I Have Them?

It may seem ironic that the same signs that signal conception—brain fog, nausea, fatigue, breast tenderness, and of course skipped periods—can also indicate declining fertility or menopause. But that’s because both are a result of hormones surging and/or plummeting. “It’s the fluctuation that causes the symptoms,” says Dr. Mysore.

So if you start feeling any pregnancy-like symptoms and haven’t reached menopause, don’t just assume they’re perimenopause. “If you have been having sex without contraception with a person who can get you pregnant, be on the safe side and take a pregnancy test, for peace of mind,” says Dr. White. “They’re easily available.”

“If you get your periods every 28 days, and it’s now day 29 or 30 without one, you should do a pregnancy test,” adds Dr. Chrisomalis-Valasiades. “And if they’re irregular, like every couple of months, test as soon as you feel the first symptoms.”

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How Important Is Birth Control During Perimenopause?

All our experts agree that, if you’re in perimenopause and you don’t want to get pregnant, contraception is a must. Don’t fall into the trap of thinking the odds of conception are negligible.

“There’s still a chance you could get pregnant, so we like to have contraception on board,” says Dr. Mysore. On top of that, she says, hormonal contraception “is very helpful to manage some of the perimenopausal shifts and changes and symptoms, especially if you’re thinking about an IUD, or a progesterone IUD.”

Dr. Chrisomalis-Valasiades’s go-to mode for perimenopausal women is a low-estrogen birth-control pill. “You can’t drop the ball in your 40s—you have to be on birth control if you really don’t want to be pregnant. But a low-dose pill, like a 10-mic pill, is perfect,” she says. “It’ll also take away some of the vaginal dryness, some of the irritability, and the brain fog.”

If committing to long-term contraception doesn’t appeal right now, there are other options. “If someone isn’t open to late-in-life pregnancy or condoms, and they’re not having sex very often, we’re really encouraging use of emergency contraception,” says Dr. White. It’s an option many women don’t consider, perhaps because of its branding—doctors are increasingly preferring the term “post-coital” contraception so as not to suggest that conditions need to be dire for it to be used. “I have patients of all ages who don’t like taking birth control every day or every week or every month when they’re not sexually active all the time. Whatever works for you in your life to prevent a pregnancy you don’t want is a great thing.”

And just as you can make preventing pregnancy work for you, there are many ways to keep perimenopause from impacting your life negatively. So whether you’re concerned about pregnancy or not, if perimenopausal symptoms are bothering you, see your obstetrician. “There are over 100 symptoms of perimenopause and menopause; there is no ‘one cocktail fits all,’” says Dr. White. “Depending on what your particular flavor of symptoms are, your doctors can advise dietary changes, medications, and different lifestyle adaptations based on where you are in your journey.”