So many health-related rumors about pregnancy seem to stick whether or not they have any basis in, you know, actual medicine. A big one you may have heard: Morning sickness means something good about the health of your pregnancy, even though it obviously feels horrid in the moment.
It’s a nice thing to think about when your head feels permanently glued to the toilet, but is this actually legit? We talked to ob/gyns and dug through the research for the truth.
Good sign or not, one thing is clear: Morning sickness can be a truly sucky experience.
Morning sickness, or nausea and vomiting during pregnancy that is estimated to affect up to 80 percent of pregnant people, usually starts before nine weeks of gestation, according to the American College of Obstetricians and Gynecologists (ACOG).
“How much morning sickness you have and how severe it is really [vary],” Christine Greves, M.D., a board-certified ob/gyn at the Winnie Palmer Hospital for Women and Babies, tells SELF. For some, morning sickness lasts for a few weeks or months, ACOG says. For an unlucky few, it lasts the whole pregnancy. And, although the “morning sickness” moniker is catchy, it’s not always accurate since you can experience pregnancy-related nausea and vomiting at any time.
It’s hard to say what, exactly, causes morning sickness, but doctors generally think it comes down to hormonal shifts. “The most accepted theory relates to a rise in two hormones during pregnancy: human chorionic gonadotropin (hCG) and estrogen,” Megan Quimper, M.D., an ob/gyn at The Ohio State University Wexner Medical Center, tells SELF.
HCG is secreted by the placenta, the organ your body creates during pregnancy to nourish the fetus via the umbilical cord. This hormone peaks in early pregnancy, which is when morning sickness is usually at its worst, Dr. Quimper explains. The placenta also produces estrogen, which increases during pregnancy and seems to contribute to morning sickness, Dr. Greves says.
Some pregnant people—up to 3 percent—experience the most severe form of morning sickness, called hyperemesis gravidarum.
A doctor can diagnose you with hyperemesis gravidarum if you’ve lost at least 5 percent of your pre-pregnancy weight due to morning sickness and are having symptoms related to severe dehydration, ACOG says.
Just like morning sickness, doctors aren’t 100 percent sure why hyperemesis gravidarum happens in some people, but experts are investigating the theory that there’s a genetic link. ACOG also says that being pregnant with multiples, having a history of hyperemesis gravidarum, having a history of motion sickness or migraines, and being pregnant with a fetus that will be assigned female at birth may also raise your risk.
While some evidence suggests that morning sickness is linked with a reduced risk of some pregnancy complications, there’s not enough proof to say it “means” much either way.
As a basic rule, having morning sickness typically indicates that a shift in hormones is taking place to sustain a pregnancy, Iffath Hoskins, M.D., clinical professor in the department of obstetrics and gynecology at NYU Langone Health, tells SELF. (There are some exceptions, like if you have underlying conditions such as thyroid or liver disease that can cause unrelated nausea and vomiting while pregnant, the Mayo Clinic says.)
But some experts believe that in addition to signaling hormonal shifts, morning sickness may offer some kind of defensive effect against pregnancy complications like miscarriage and preterm labor. However, the research to back up these claims is varied and not conclusive, so scientists aren’t yet sure whether or not this effect is real.
A 2016 study published in JAMA Internal Medicine analyzed data from 797 pregnant people in the United States who had previously experienced one or two miscarriages. The study authors found that morning sickness in early pregnancy seemed to have a “protective association” that resulted in a 50 to 75 percent reduced risk of miscarriage. Experts aren’t sure why this possible protective effect may exist, but one theory is that the nausea and vomiting represent that a viable placenta with sufficient hormones is supporting the fetus.
A 2018 study published in BMC Pregnancy & Childbirth analyzed data from 96,056 pregnant people in Japan, finding that those who didn’t experience morning sickness had a slightly higher rate of preterm births, while those who had severe morning sickness had the lowest risk. People with morning sickness also experienced fewer instances of issues like pregnancy-induced hypertension. Interestingly enough, though, people with morning sickness experienced higher rates of “threatened abortion” (vaginal bleeding with or without abdominal cramps in the first trimester) and “threatened premature labor” (experiencing contractions before 37 weeks).
There’s a similarly interesting variation in a 2015 BMC Pregnancy & Childbirth study that examined 51,675 pregnant people in Norway, finding that those who experienced at least some nausea and vomiting during pregnancy had higher odds of complications like hypertension and preeclampsia than their symptom-free counterparts, but lower odds of issues like preterm birth and low birth weight.
There are clearly a few intriguing potential links between morning sickness and maternal and fetal health, but science hasn’t determined anything definitive so far. It’s hard to prove cause and effect for any of these claims. The fact that so many people experience morning sickness makes it a tricky thing to study, Dr. Greves says. Think of all the variables involved that researchers need to rule out in order to truly investigate only the effect of morning sickness on pregnancy and childbirth without including any other factors. Various studies also point to an inconsistent research classification of nausea and vomiting during pregnancy as a complicating issue.
Ultimately, the point is that there’s no medical reason to think morning sickness is automatically a “good” or “bad” thing. It’s just a thing that happens to many people while pregnant.
There’s also no scientific reason to think that a lack of morning sickness is cause for concern.
“If you are not experiencing morning sickness, this does not mean the pregnancy is unhealthy,” Dr. Quimper says. Experts don’t know why some people experience morning sickness and others don’t, but sailing through pregnancy without nausea and vomiting doesn’t automatically mean anything is wrong.
The only thing that can really be “wrong” when it comes to morning sickness is if you have hyperemesis gravidarum, because that means your nausea and vomiting are too severe. If you think you have hyperemesis gravidarum, you need to talk to your doctor about being especially on top of your health, nutrition, and hydration. First of all, it may help make you less miserable. Beyond that, the relentless nausea and vomiting can make it hard to get enough calories, which can theoretically negatively impact the fetus’s growth in severe cases, Dr. Hoskins points out.
With that said, the link here is also not definitive, as this 2017 Pharmacology review of 81 related studies explains, so you don’t need to immediately be concerned that having hyperemesis gravidarum could affect your baby. “This illness alone does not typically affect the health of your baby as pregnancies are very resilient,” Dr. Quimper says. But talk to your doctor anyway. If you do have hyperemesis gravidarum, you may benefit from IV treatment and anti-nausea medications.
The takeaway: It’s entirely possible—and common—to have a healthy baby even if you have the most severe version of morning sickness. It’s also completely possible—and, again, common—to have a healthy baby if you don’t experience morning sickness at all. But if you’re concerned about your level of morning sickness or anything else about your pregnancy, it’s always a good idea to check in with your doctor.