Morning sickness is the nausea and vomiting that most pregnant people experience during the first trimester, typically starting around week six and peaking between weeks eight and ten. Despite the name, it can strike at any hour. Symptoms usually improve or resolve by week 13, though a smaller number of people deal with nausea well into the second trimester or beyond.
Why It Happens
For decades, researchers linked morning sickness to rising levels of pregnancy hormones without pinpointing a clear mechanism. Recent work from the University of Cambridge has identified the main culprit: a protein called GDF15, produced by the fetal side of the placenta and released into the mother’s bloodstream. GDF15 acts on a specific receptor in the brain that triggers nausea and suppresses appetite. The severity of symptoms depends on two things: how much GDF15 the placenta produces and how sensitive the mother’s body is to it.
That sensitivity is shaped by what your body was used to before pregnancy. GDF15 circulates at low levels in everyone, and people who naturally had very low levels before conceiving tend to react more strongly when the placenta floods their system with it. Researchers confirmed this by studying women with beta thalassemia, an inherited blood disorder that keeps GDF15 levels chronically high. Those women reported dramatically less nausea and vomiting during pregnancy because their brains were already accustomed to the hormone. On the flip side, people carrying certain genetic variants that cut their baseline GDF15 by up to 50% face a much higher risk of severe pregnancy sickness.
What It Feels Like Day to Day
Morning sickness ranges from mild queasiness to relentless nausea that makes it hard to eat, work, or function normally. Some people vomit once or twice a day; others feel constantly nauseated without ever actually throwing up. Certain smells, textures, or even the thought of particular foods can set it off. Fatigue often compounds the experience, and the combination can affect both physical and mental well-being. Early pregnancy nausea has been linked to higher rates of depressive symptoms, and women who experience daily nausea consistently score lower on measures of mental health compared to those without symptoms.
The practical toll is significant. In the United Kingdom alone, researchers estimated that nausea and vomiting in pregnancy account for roughly 8.6 million lost hours of paid work and 5.8 million lost hours of housework each year. About 25% of affected women report markedly impaired job performance. This isn’t a minor inconvenience for many people; it reshapes daily life for weeks.
When Morning Sickness Becomes Hyperemesis Gravidarum
A small percentage of pregnant people develop a severe form called hyperemesis gravidarum (HG). The key distinction is weight loss: if you lose more than 5% of your pre-pregnancy weight from vomiting and an inability to keep food or fluids down, that crosses into HG territory. Other warning signs include dark urine, dry skin, weakness, lightheadedness, fainting, and being unable to tolerate any fluids for more than 12 hours. HG sometimes requires medical treatment to correct dehydration and nutritional deficits, and it can persist longer than typical morning sickness.
The same GDF15 mechanism appears to drive HG, just at a more extreme level. People with genetic variants that lower their baseline GDF15 are disproportionately represented among HG cases, which helps explain why the condition runs in families.
Does Morning Sickness Affect the Baby?
Typical morning sickness does not harm the developing baby. In fact, studies have found that pregnant people who experience first-trimester nausea and vomiting have a lower risk of miscarriage compared to those who don’t. Researchers aren’t entirely sure why, but the association has held up across multiple studies. This doesn’t mean that a symptom-free pregnancy is cause for concern. It simply means that nausea, while miserable, appears to correlate with a healthy early pregnancy in most cases.
Severe, prolonged vomiting that leads to significant weight loss and dehydration is a different story. When the body can’t hold onto enough nutrients and fluids, that can affect fetal growth, which is why HG warrants medical attention.
Managing Symptoms Through Diet
What you eat can meaningfully influence how sick you feel. Protein-rich foods, including meat, fish, and eggs, appear to have a protective effect. One study found a 37% reduction in the risk of severe pregnancy sickness among women who regularly consumed these foods, with three to four servings of fish per week showing a particularly strong association. Protein stabilizes blood sugar and takes longer to digest, which may help keep nausea at bay compared to eating on an empty stomach or relying on simple carbohydrates alone.
Interestingly, women experiencing morning sickness tend to consume significantly more simple sugars, likely because sweet snacks and drinks provide quick energy and feel easier to tolerate in the moment. Cross-cultural data supports this pattern: populations with higher rates of pregnancy nausea also consume more simple sugars from sweetened beverages and snacks. Whether sugary foods genuinely relieve symptoms short-term or simply reflect a shift in food preferences during nausea isn’t fully settled, but the overall evidence favors leaning toward protein when you can manage it.
A few practical strategies that many people find helpful:
- Eat small, frequent meals rather than three large ones, so your stomach is never completely empty or overly full.
- Keep bland snacks nearby for first thing in the morning, before nausea has a chance to build.
- Stay hydrated in small sips throughout the day, especially if vomiting is frequent.
- Avoid strong smells and foods with intense flavors or textures that trigger your nausea.
Who Gets It Worse
About seven in ten pregnant people experience some degree of nausea, so it’s far more common to have it than not. Several factors can increase your odds of more severe symptoms. A family history of morning sickness or HG raises your risk, which aligns with the genetic findings around GDF15 sensitivity. People carrying twins or higher-order multiples often experience worse nausea, likely because the placenta produces more GDF15. A history of motion sickness or migraine-related nausea also seems to make pregnancy nausea more intense, possibly because the brain’s nausea pathways are already more reactive.
First pregnancies can go either way, but if you had significant morning sickness in a previous pregnancy, you’re likely to experience it again. The severity isn’t always identical, though, since each pregnancy involves a different placenta producing different amounts of GDF15.