Morning sickness happens because of a hormone called GDF15 that rises sharply in early pregnancy. Your body’s sensitivity to this hormone determines how severe your symptoms get. Research from the University of Cambridge and other institutions has pinned down the main biological cause. It is not psychological or caused by a weak stomach. It is a real physical response to a specific hormone.
What Exactly Is GDF15 and How Does It Trigger Nausea?
GDF15 stands for Growth Differentiation Factor 15. It is a hormone that your body produces in small amounts normally. During pregnancy the placenta starts making large amounts of it. The hormone acts on a specific part of your brain called the area postrema. That area controls nausea and vomiting.
Your sensitivity to GDF15 matters more than how much of it you have. Some women have naturally low sensitivity. They barely feel sick even with high GDF15 levels. Other women have high sensitivity. Even small increases make them very ill. This explains why two women with the same pregnancy hormone levels can have completely different experiences.
Research published in Nature in 2023 showed that women with a genetic variant that lowers GDF15 sensitivity are less likely to have severe morning sickness. Women with a different variant that makes them more sensitive are more likely to need hospital care for hyperemesis gravidarum. That is the extreme form of morning sickness that causes dangerous weight loss and dehydration.
Does What Causes Morning Sickness During Pregnancy Affect Everyone the Same Way?
No. The severity varies widely from person to person. About 70 to 80 percent of pregnant women have some nausea or vomiting. The CDC reports that about 2 percent of pregnant women develop hyperemesis gravidarum. That is the severe form that requires medical treatment.
Your genetics play a big role. If your mother or sister had severe morning sickness you are more likely to have it too. Your body weight before pregnancy also matters. Women with a lower body mass index tend to have more nausea. Women with a higher BMI often report less.
The timing is very predictable for most women. Nausea usually starts around week 6 of pregnancy. It peaks between weeks 8 and 10. It typically goes away by weeks 14 to 16. Some women feel sick longer. A small number have nausea throughout their entire pregnancy. That is unusual but it happens.
What Other Factors Can Make Morning Sickness Worse?
Several things can increase nausea even if they do not cause it on their own. Strong smells are a common trigger. Cooking odors perfume and cigarette smoke can set off a wave of nausea. An empty stomach also makes symptoms worse. Low blood sugar can trigger the nausea center in your brain.
Stress and fatigue can amplify symptoms. Your body is already working hard to grow a placenta and support a new life. Adding physical or emotional stress on top of that can make the nausea harder to manage. This does not mean morning sickness is caused by stress. But stress can make an existing biological response stronger.
Some studies suggest that women carrying twins or triplets have higher GDF15 levels. This often leads to more severe nausea. Women with a history of motion sickness or migraines also tend to report worse morning sickness. These conditions may share some of the same brain pathways that respond to GDF15.
What Actually Works to Reduce Morning Sickness?
The evidence supports a few specific approaches. The American College of Obstetricians and Gynecologists recommends these strategies:
| Intervention | Evidence Level | How It Helps |
|---|---|---|
| Vitamin B6 with doxylamine | Strong | Reduces nausea by affecting brain chemicals that trigger vomiting |
| Ginger | Moderate | May calm the digestive tract and reduce nausea signals |
| Eating small frequent meals | Moderate | Prevents low blood sugar and keeps stomach partially full |
| Acupressure wristbands | Weak | Some people report benefit but studies show mixed results |
Vitamin B6 combined with doxylamine is the only medication specifically approved by the FDA for morning sickness. It is sold under the brand name Diclegis in the United States. Many women take over-the-counter vitamin B6 and Unisom separately. This works the same way and costs less.
Ginger has real evidence behind it. Studies show it reduces nausea as effectively as vitamin B6 for some women. You can take it as tea capsules or chews. Stick to about 1 gram per day. More than that can cause heartburn.
What Should You Avoid When Trying to Manage Morning Sickness?
Do not take anti-nausea medications without talking to your doctor first. Some common over-the-counter nausea drugs are not safe during pregnancy. Meclizine and promethazine require a doctor’s approval. Never take any medication that contains aspirin or ibuprofen for nausea. These can harm the baby.
Do not force yourself to eat foods that make you sick. Many well-meaning people suggest bland crackers or plain toast. If those foods trigger your nausea do not eat them. Eat whatever sounds tolerable. Some women can only eat cold foods like fruit or yogurt. Others do best with salty snacks. Your body will tell you what works.
Do not worry about nutrition for a few weeks. If you can only eat potatoes and applesauce for two weeks that is fine. Your baby will take what it needs from your body. The placenta is a very efficient organ. The biggest concern is staying hydrated. If you cannot keep liquids down for 12 hours call your doctor. If you cannot urinate or your urine is dark you need medical attention.
When Should You See a Doctor for Morning Sickness?
You should call your doctor if you cannot keep any food or liquid down for 24 hours. You should also call if you lose more than 5 percent of your pre-pregnancy body weight. The CDC defines hyperemesis gravidarum as severe nausea and vomiting that causes weight loss and dehydration.
Other warning signs include vomiting blood. That can mean you have torn the lining of your esophagus from forceful vomiting. It looks like coffee grounds when it comes up. You should also seek help if you feel faint or dizzy when standing up. That is a sign of dehydration.
Severe morning sickness is treatable. Doctors can prescribe stronger anti-nausea medications that are safe during pregnancy. Some women need IV fluids in a hospital or clinic. A small number need a feeding tube for nutrition. These treatments are not common but they exist for a reason. Do not suffer in silence thinking morning sickness is something you must endure.
What Is the One Thing Most People Get Wrong About Morning Sickness?
The name is misleading. Morning sickness does not only happen in the morning. A study in the journal Obstetrics & Gynecology found that only about 30 percent of women have symptoms limited to morning hours. Most women feel sick throughout the day. Some feel worse at night.
The name also makes it sound mild. For many women it is not mild. It can interfere with work sleep and basic daily life. Calling it morning sickness minimizes what women actually experience. The medical term is nausea and vomiting of pregnancy or NVP. That is more accurate and less dismissive.
Another common myth is that morning sickness means the baby is healthy or that lack of nausea means something is wrong. Neither is true. Some healthy pregnancies have no nausea at all. Some pregnancies with severe nausea end in miscarriage. Nausea is not a reliable sign of pregnancy health. It is just a biological response to hormones.
Frequently Asked Questions
Can morning sickness hurt my baby?
Mild to moderate morning sickness does not harm your baby. Severe vomiting that causes weight loss and dehydration can affect the baby and needs medical treatment.
Does morning sickness get worse with each pregnancy?
Not necessarily. Some women have worse symptoms in later pregnancies. Others find it gets better. There is no predictable pattern from one pregnancy to the next.
Can what I eat cause morning sickness?
Food does not cause morning sickness. The hormone GDF15 causes it. But certain foods and smells can trigger nausea once you are already sensitive.
When does morning sickness end for most women?
Most women feel better by week 14 to 16 of pregnancy. Some women have symptoms that last longer. A small number have nausea throughout the entire pregnancy.
