Morning sickness is one of the most common experiences during pregnancy, affecting up to 80% of expectant mothers. Despite its name, this condition can strike at any time of day or night, bringing waves of nausea and vomiting that can last for weeks or even months. While it’s usually harmless to the baby, morning sickness can significantly impact daily life, making it essential to understand what causes it and how to manage it effectively.
Epidemiology
Morning sickness is incredibly common among pregnant women worldwide. Research shows that between 50% and 80% of all pregnant women experience some degree of nausea and vomiting during pregnancy, with most studies suggesting that around 70% of women are affected.[1][2][5]
The condition typically begins early in pregnancy, usually around the fourth to sixth week after conception. Most women notice symptoms before nine weeks of pregnancy have passed.[2][3] The symptoms tend to feel worst around eight to ten weeks of pregnancy, when hormone levels are at their peak.[2]
For the majority of women, morning sickness improves or disappears entirely by the end of the first trimester (the first three months of pregnancy), typically around weeks 12 to 16.[1][3] However, about one in five women continues to experience symptoms into the second trimester, and a small number of women endure nausea and vomiting throughout their entire pregnancy.[3][5]
A severe form of morning sickness, called hyperemesis gravidarum, affects approximately 2% to 3% of pregnant women.[1][5][10] This condition is characterized by extreme nausea and vomiting that can lead to dangerous weight loss and dehydration (when the body doesn’t have enough water), often requiring hospital treatment.[2]
Causes
The exact cause of morning sickness remains something of a medical mystery, though researchers have made significant progress in understanding what triggers this uncomfortable condition. The prevailing belief is that morning sickness results from a combination of physical and chemical changes happening in the body during early pregnancy.[2][3]
Hormonal changes during the first trimester are thought to play a major role. Pregnancy brings dramatic increases in several hormones, including human chorionic gonadotropin (hCG), estrogen, and progesterone.[2] These hormones are essential for maintaining a healthy pregnancy, but they also appear to trigger nausea in many women. The timing of morning sickness aligns closely with when hCG levels peak in early pregnancy, suggesting a strong connection.[19]
A groundbreaking study published in 2023 identified a specific hormone called GDF15 as a key cause of pregnancy sickness. This hormone is produced by the fetus and the placenta (the organ that grows in the uterus to supply the baby with food and oxygen).[4] Researchers found that women exposed to lower levels of GDF15 before pregnancy tend to experience more severe symptoms when the hormone suddenly increases during pregnancy. This discovery suggests that a woman’s sensitivity to GDF15, rather than just the hormone level itself, determines how sick she becomes.[4]
Other factors that may contribute to morning sickness include low blood sugar levels, fluctuations in blood pressure (particularly lowered blood pressure), and changes in how the body metabolizes (processes) carbohydrates.[2][3] The enormous physical and chemical transformations that pregnancy triggers throughout the body may also play a role in causing nausea and vomiting.[3]
Risk Factors
While morning sickness can affect any pregnant woman, certain factors increase the likelihood of experiencing symptoms. Understanding these risk factors can help women prepare for what might lie ahead during their pregnancy.
Women carrying multiple babies, such as twins or triplets, face a higher risk of morning sickness.[5][10] This is likely because the placenta is larger in multiple pregnancies, leading to increased production of pregnancy hormones that trigger nausea.[5] Additionally, women pregnant with a girl appear to be slightly more likely to experience severe morning sickness than those carrying boys.[5]
A personal or family history of morning sickness significantly increases risk. If a woman experienced morning sickness in a previous pregnancy, whether mild or severe, she’s more likely to have it again in future pregnancies.[5][11] Similarly, if a woman’s mother or sister had severe morning sickness, her chances of experiencing it increase.[5][11]
Women who are prone to motion sickness or suffer from migraine headaches (severe headaches that may cause sensitivity to bright lights and sound) tend to experience more morning sickness.[5][10][11] First-time mothers also appear to be at higher risk, possibly because their bodies haven’t previously adapted to the surge of pregnancy hormones.[11][19]
Being overweight or obese before pregnancy increases the risk of morning sickness.[5][11] Women who previously felt nauseous when taking birth control pills containing estrogen may also be more susceptible to pregnancy-related nausea.[11]
Rarely, certain medical conditions can cause nausea and vomiting during pregnancy that may be mistaken for morning sickness. These include stomach ulcers, food-related illnesses, thyroid or gallbladder disease, and urinary tract infections.[7][10] Healthcare providers will look for additional symptoms that don’t typically occur with morning sickness to rule out these conditions.[10]
Symptoms
The hallmark symptoms of morning sickness are nausea and vomiting, but the experience varies considerably from woman to woman. Some women feel mildly queasy for a short time each day, while others battle severe nausea that lasts all day long.[2][10]
Common symptoms include an upset stomach, loss of appetite, and vomiting. Women describe the sensation in different ways—some say it feels like heartburn or reflux, others compare it to seasickness or motion sickness. Some women feel as if something is stuck in their throat, while others experience sensations similar to hunger pangs even when they’re not hungry.[2]
Despite its name, morning sickness can strike at any time of day or night. While symptoms are often worse early in the day (hence the name), many women feel sick throughout the entire day.[1][2][5] The unpredictability of symptoms can make planning daily activities challenging.
Certain triggers often make symptoms worse. Many pregnant women develop a heightened sense of smell, and certain odors that never bothered them before can suddenly trigger intense nausea.[1][2] Eating or even smelling certain foods may provoke vomiting. Other factors that can worsen morning sickness include stress and anxiety, being overtired, heat or warm weather, and motion sickness.[2]
When morning sickness becomes severe, it crosses into the territory of hyperemesis gravidarum. Warning signs include vomiting more than three or four times per day, inability to keep food or liquids down for 24 hours, producing little to no urine or urine that is dark in color, feeling dizzy or faint when standing up, having a racing or pounding heartbeat, and losing more than 5% of pre-pregnancy body weight.[1][2][10]
Beyond physical symptoms, morning sickness can take a toll on mental health. The condition can prevent women from working, socializing, and caring for other children. Studies show that pregnant women enduring morning sickness report higher levels of psychological stress, including anxiety and depression.[3] For years, some people falsely believed that morning sickness was purely psychological—that women’s fears and anxieties triggered their physical discomfort. However, there is no research to support these claims, and morning sickness is now recognized as a real physical condition with biological causes.[3]
Prevention
While there’s no guaranteed way to prevent morning sickness entirely, emerging research offers hope for reducing symptoms in future pregnancies. The discovery that GDF15 sensitivity plays a key role in causing morning sickness has opened up potential prevention strategies.
Scientists suggest that exposing women to GDF15 before pregnancy might help “prime” their bodies to tolerate higher levels of the hormone once they become pregnant.[4] This preparation could potentially reduce the severity of symptoms. However, this approach is still in the research stage and not yet available as a standard prevention method.
For women who have experienced morning sickness in previous pregnancies, being prepared can make a difference. Knowing what to expect and having management strategies ready from the start can help minimize the impact on daily life. Working with a healthcare provider to develop a plan before becoming pregnant again may be beneficial, especially for women who previously experienced hyperemesis gravidarum.
Once pregnancy begins, certain lifestyle measures may help prevent symptoms from worsening. Getting plenty of rest is crucial, as tiredness can make nausea worse.[11] Avoiding known triggers, such as strong smells or certain foods, can also help. Eating small, frequent meals rather than large ones may prevent the stomach from becoming too empty or too full, both of which can trigger nausea.[2]
Some women find that keeping crackers or dry toast by the bedside and eating a few before getting out of bed in the morning helps settle the stomach.[2][11] Taking prenatal vitamins at night with a small amount of food, rather than on an empty stomach in the morning, may also reduce nausea for some women.[14]
Pathophysiology
Understanding what happens in the body during morning sickness helps explain why symptoms occur and how treatments work. Pathophysiology refers to the changes in normal body functions that occur during disease or in this case, a pregnancy-related condition.
During pregnancy, hormone levels rise dramatically. The placenta produces large amounts of hCG, particularly during the first trimester. This hormone is essential for maintaining pregnancy, but it also appears to affect the part of the brain that controls nausea and vomiting.[19] Estrogen and progesterone levels also increase substantially. Progesterone relaxes the muscles of the digestive tract, which makes digestion less efficient and can contribute to feelings of nausea and reflux.[19]
The recent discovery about GDF15 has provided the clearest picture yet of morning sickness pathophysiology. This hormone is produced by the fetus and increases substantially during pregnancy.[4] GDF15 is normally released by different areas of the body in response to stress, and it acts on receptors in the part of the brain that controls nausea and vomiting.[15]
Research shows that women who have lower levels of GDF15 in their bodies before pregnancy are more sensitive to the sudden increase in this hormone when they become pregnant. This sensitivity triggers more severe nausea and vomiting.[4] Interestingly, if the baby inherits a genetic mutation that causes low GDF15 production, the mother may experience less severe symptoms because the overall hormone levels remain lower.[4]
Blood pressure fluctuations, particularly lowered blood pressure, may also contribute to morning sickness symptoms.[2][3] Additionally, changes in how the body processes carbohydrates and maintains blood sugar levels during pregnancy may play a role. Low blood sugar has been identified as a possible trigger for nausea.[2]
When morning sickness progresses to hyperemesis gravidarum, additional physiological changes occur. Frequent vomiting leads to dehydration and an imbalance of electrolytes (minerals like sodium and potassium that help the body function properly).[8] This dehydration can affect kidney function and, if severe enough, may require hospital treatment with intravenous fluids to restore proper hydration and electrolyte balance.[1]
Some women worry that the physical act of vomiting might harm the baby. However, the fetus is perfectly cushioned inside its sac of amniotic fluid (the protective liquid surrounding the baby in the womb).[3] Vomiting and retching may strain the abdominal muscles and cause localized aching and soreness for the mother, but the physical mechanics of vomiting won’t harm the developing baby.[3]
Studies have consistently shown that mild to moderate morning sickness does not harm the unborn child.[6] Mild weight loss during the first trimester is common when women have moderate symptoms and is not harmful to the baby.[6] However, severe morning sickness that includes significant weight loss and dehydration requires prompt medical attention to prevent complications for both mother and baby.[3]