WTH?! (What The Health?!) is a Scary Mommy series that will answer health questions relevant to moms and women that we don’t talk about enough. Think: “What is this weird pregnancy symptom? WTF is happening to me postpartum? Are these signs of perimenopause?” Let’s normalize these and other women’s health issues by talking about them more in a relatable, less clinical, and no-BS way.

Welcome to your 40s. Your periods are about to take you for a wild ride.

As Jancee Dunn, author of Hot and Bothered: What No One Tells You About Menopause and How to Feel Like Yourself Again, told Scary Mommy: “One month, [my period] was this tiny little trickle, like a teeny little tributary. And the next, it was like Victoria Falls.”

And she’s not the only one to deal with erratic periods in her 40s. When we polled our readers, it was clear what a wide range of symptoms women experience: “I’m 47 and get worse cramps than when I was a teenager.” “It’s almost nothing now. It looks like it’s drying.” “They keep coming earlier and earlier.” “Mine comes once in a blue moon with a vengeance.” “Some lighter, some heavier… totally unpredictable.” “WTF is happening?!?!”

Scary Mommy talked to OB-GYNs about the unexpected ways periods change during this decade, why this happens, and what you can do about it.

Your periods will probably become “irregularly irregular.”

“Some people have a change in the interval [the time between periods]. Some people see a different amount of bleeding. And some people will experience intermenstrual bleeding [like two periods a month],” says Dr. Michael Krychman, VP of Medical Affairs at HerMD.

In other words, your periods may go completely haywire. They may have previously lasted seven days, and now they’re only three days. You may bleed between periods or skip a period altogether.

“Even in women who said, ‘I always had super easy periods’… they can become really heavy, sporadic, and full of clots,” says Dr. Heather Hirsch, founder of the Menopause and Midlife Clinic at Brigham and Women’s Hospital and author of Unlock Your Menopause Type.

There is a major culprit that causes these inconsistent periods.

And that culprit is often perimenopause, which starts for many women in their 40s, and is a huge driver of changing periods.

“I was 45, and I skipped a few periods… I thought, ‘Oh, oh my God, I’m pregnant,’” Dunn says. “I had a toddler, and I was in like mommy and me land… I just wasn’t thinking about menopause.”

Perimenopause is often described as puberty in reverse. “We probably have all blocked out puberty or the beginning of our periods, but they’re kind of a sh*t storm. And that sh*t storm comes back,” Hirsch says.

Hirsch explains that, during perimenopause, hormones are winding down, whereas in puberty they’re winding up. The changes in the hormones estrogen and progesterone are what cause these irregular periods.

“Progesterone is the ‘glue’ that holds the uterine lining together and kind of creates this synchrony of beautiful periods for the 27-year-old who gets them like clockwork,” she says. And for a lot of women going through perimenopause, progesterone actually declines earlier than estrogen, which can cause these heavy, clot-filled periods.

Some other signs that may indicate you’re going through perimenopause can include vaginal dryness, hot flashes, and sleep problems (fun stuff!). The good news is this doesn’t last forever. Once you’ve missed 12 periods in a row, you know you have officially entered menopause, according to the Mayo Clinic.

There are other conditions to watch out for.

While perimenopause often occurs in your 40s, some women may experience it earlier or later, so this may not necessarily be the cause for your irregular periods. Dr. Erica Montes, creator of The Modern Mujer, says there are some other conditions that can be common during this age range and diagnosed by an OB/GYN: adenomyosis (when the lining inside the uterus grows into the muscle layer of the uterus), uterine fibroids (growths that form from the muscle tissue of the uterus), endometrial polyps (growths that are attached to the wall of the uterus), and PCOS (a hormone imbalance).

You don’t have to just suffer through bad periods. Here’s when to get help.

Hirsch recommends tracking your period in a journal or period tracker so you know what’s “normal” for you and when your periods may start to appear “irregular.” (She likes using the balance app, which is geared toward perimenopause and menopause.)

If you notice your periods are lasting a long time (more than one to two weeks), are less than 25 days apart or more than 35, or are changing a lot from your baseline, it’s a good time to see a doctor. They can determine if you need an ultrasound or biopsy to rule out other conditions.

“If [women are] feeling like their hormones are in chaos or they’re fluctuating between normal and abnormal periods, they should seek [help] and not minimize,” Krychman says. “It’s very important…[they] know that they don’t have to suffer in silence.”

Read our other WTH articles:

What No One Tells You About Peeing After Having Kids