And no, it's not just an a.m. affliction.
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Pregnancy is seldom a total cake walk, and one of the most persistent issues many women face is morning sickness -- the classic pregnancy symptom characterized by vomiting and nausea that renders them unable to stomach anything beyond, say, one-eighth of a dry cracker and two sips of water. And it affects a lot of women: studies estimate that anywhere between 70 and 90 percent of women experience some degree of morning sickness. Here are the basics:

There’s no clear definition.

"Morning sickness" isn't an official diagnosis -- and it's also a complete misnomer, because it can strike women at any point during the day (and in some cases, feels a lot more like 24/7 sickness). Doctors and midwives generally prefer the term "nausea and vomiting of pregnancy," which is intentionally broad. "There's not a strict definition," Dr. Patricia Robertson, a professor in the department of obstetrics and gynecology and reproductive sciences with the University of California, San Francisco, told The Huffington Post. Which means that for some women, morning sickness will manifest itself as a mild but unrelenting queasiness; other women will throw up multiple times a day. Food aversions are also a common symptom.

"Most women," Robertson said, "will have some nausea during pregnancy."

We still don’t know what causes it.

Researchers have looked into the question of what causes morning sickness, but -- even though women have been dealing with it since forever -- they’re still not entirely sure. The leading hypothesis is that increasing levels of certain hormones play a key role.

"We think it may happen because of the increased presence of one of the main pregnancy hormones, hCG," Nicole Lassiter, a nurse-midwife and professor at Frontier Nursing University told HuffPost. "There is a correlation between when hCG levels are the highest and when 'normal' nausea and vomiting of pregnancy peaks -- around 11 weeks." There may also be a genetic component to why some women experience morning sickness, she added, and some studies suggest those who had it with one baby are more likely to experience it again with subsequent pregnancies, although that's certainly not a given.

It’s generally pretty short-lived (though it may not feel that way).

Morning sickness is often one of the first symptoms of pregnancy women notice after they miss their period, Lassiter said, alongside other gems, like breast tenderness and fatigue. It's fairly common for it to rear its ugly head around 6 to 8 weeks gestational age, she explained, peak around 11 weeks (which is also when hCG levels peak) and start to go away around 14 weeks or so. It probably feels like it lasts a whole lot longer when you're in the throes of it, though.

“Sometimes, it lasts for as long as 16 to 20 weeks, but for most women, symptoms are going to diminish or resolve completely by early in the second trimester,” Lassiter said. If nausea and vomiting start later in a pregnancy, or last for longer than expected, those are issues women should absolutely raise with their providers, Lassiter added, as they may be a sign that something more serious is going on.

Non-pharmacological treatments can help.

Women with relatively mild morning sickness (more on what that means below) may benefit from any number of lifestyle strategies to help get their nausea under control. One of the first things women can do is simply make sure to eat every hour and a half or so, Lassiter said -- preferably, something somewhat nutritious with some protein, but really, whatever they can get, and keep, down.

“It’s counterintuitive, but an empty stomach can contribute to nausea, so having something to eat can make a big difference,” Lassiter said, adding that it’s especially important for women to eat something with protein before they go to bed at night if they can, so they don’t wake up hungry and nauseated. (Indeed, some women may experience more symptoms in the morning simply because they have an empty stomach, hence "morning" sickness.)

Ginger is another option, and women can eat it raw or take it in capsule form. “There are now ginger popsicles you can lick," Robertson said, adding that women may also benefit from acupressure. Products like Sea Bands, which are worn on the wrist, have a hard knob that gently presses on a specific point that may provide some women with relief while they're wearing them.

More serious cases may require more serious intervention.

For women with more serious morning sickness -- so, those who find their nausea is unrelenting and debilitating, or women who vomit multiple times a day and may even be losing weight -- medication can make a big difference. The American College of Obstetricians and Gynecologists says that a prescription medication that is a combination of doxylamine, an antihistamine, and vitamin B6 is considered safe and effective, and should be a first-line treatment option for women.

Up to 2 percent of pregnant women experience Hyperemesis Gravidarum, which is morning sickness so severe they can't keep down foods or fluids (otherwise known as what Kate Middleton had). Like "nausea and vomiting of pregnancy," it too is a kind of diagnosis of exclusion, Lassiter said, without a clear, specific etiology. But it's extremely important to get treated to avoid dangerous complications, such as dehydration.

No matter how severe, it's okay to make "a big deal" about it.

Just because morning sickness is common, doesn't mean it's necessarily benign. Constant nausea and vomiting can take a real toll on women's quality of life -- and women should absolutely feel empowered to talk to their OB-GYN, midwife or nurse practitioner about what they're feeling early on. In fact, getting morning sickness under control early on in pregnancy may prevent more serious complications down the road that require hospitalization and IV fluids, ACOG says. Plus, care providers will want to rule out other possible causes for nausea, such as GERD or thyroid issues, Lassiter said.

"I think most women let us know that if it gets really bad -- and certainly if you're throwing up multiple times a day -- you need to check in," Robertson said.

But even if it the symptoms are less severe, "they shouldn't brush it off," she urged. Pregnant women should feel empowered to ask up for the help they need.

The more you know, mamas-to-be.

CORRECTION: An earlier version of this story incorrectly stated that HGC levels may be linked to morning sickness. The correct term is hCG.

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