Morning sickness, which involves nausea and vomiting, is one of the most common symptoms during early pregnancy. It’s estimated that 50-90% of pregnant women experience some degree of nausea and vomiting. While often called “morning sickness,” symptoms can occur at any time of day. Typically, morning sickness starts around week 6 of pregnancy and peaks around week 9. For most women, symptoms go away by weeks 14-16. But for some, nausea and vomiting can persist well into the second and third trimesters.
There are several theories as to why morning sickness occurs:
Hormonal changes
Rapidly rising levels of the hormone human chorionic gonadotropin (hCG) appear to play a role in nausea and vomiting during pregnancy. hCG levels increase steadily during the first trimester and peak around weeks 8-11. This corresponds to when symptoms are often worst. Research shows a correlation between higher hCG levels and more severe nausea and vomiting. Estrogen levels also rise during the first trimester, which may contribute.
Sensitive sense of smell
Pregnancy hormones like estrogen and hCG cause a heightened sense of smell. Smells that were once tolerable may now trigger nausea and gagging. Things like foods cooking, perfumes, cleaning products, and cigarette smoke are common culprits. This sensitive nose is thought to be an evolutionary adaptation to protect the developing baby from potentially dangerous substances.
Slowed digestion
Progesterone relaxes smooth muscles like the intestines and may cause food to digest more slowly. This can lead to nausea, vomiting, constipation, and heartburn. Slow digestion allows more time for nausea triggers to take effect.
Low blood sugar
Blood sugar levels tend to be lower during pregnancy. This can exacerbate nausea especially if meals are missed. Eating small, frequent meals and not letting yourself get overly hungry can help prevent low blood sugar levels.
Stress and fatigue
Being pregnant is a major physical and emotional adjustment. Stress, fatigue, and other lifestyle factors related to pregnancy can make nausea worse or trigger vomiting episodes. Getting plenty of rest is important.
Why the nausea and vomiting?
While the exact mechanisms are unknown, most experts believe morning sickness serves a beneficial purpose for mom and baby. Potential explanations include:
Protecting the developing embryo
Morning sickness may safeguard the early embryo from toxins and harmful food substances. Vomiting may rid the body of any dangerous ingested materials. Nausea makes certain smells and foods unappealing, which reduces exposure to potential risks.
Promoting a healthy pregnancy
Morning sickness may help indicate a healthy pregnancy with adequate hCG levels. One study found less morning sickness in women who later had miscarriages. Nausea and vomiting might signal that embryo implantation and placental function are progressing normally.
Driving dietary changes
Morning sickness drives many women to avoid certain foods and beverages. Changing the diet in this way may supply nutrients needed for fetal development and growth. Food aversions tend to target meat, fish, poultry, and eggs. Cravings often focus on dairy, citrus, vegetables, and carbohydrates.
Preventing dietary toxins
Nausea and vomiting may protect against dietary toxins that could harm the developing embryo. Many plant foods contain teratogenic and mutagenic chemicals that cross the placenta. Morning sickness steers women away from plants associated with birth defects like celery, parsley, sages, and carrots.
What causes the vomiting?
While nausea and food aversions arise from the stomach, vomiting is controlled by an area of the brain called the vomiting center. Vomiting results from direct stimulation of the vomiting center by:
Pregnancy hormones
Rising levels of hCG and estrogen in the bloodstream directly stimulate the vomiting center. As mentioned, higher blood levels of hCG tend to correspond with more severe vomiting.
Gag reflex
The sensitive gag reflex during pregnancy is triggered more easily. This sends signals to the vomiting center. Smells, gagging motions while brushing teeth, and mucus drainage can all activate the gag reflex.
Messages from the inner ear
The inner ear sends signals about motion and position changes to the brain. In pregnancy, this system becomes more sensitive. Sudden movements or spatial disorientation can trigger nausea and vomiting.
Irritation or inflammation
Issues like gastritis, gallstones, pancreatitis, urinary tract infections, and appendicitis can all stimulate the vomiting center during pregnancy. Morning sickness makes the body more susceptible to vomiting from other causes.
Risk factors
Certain factors put a woman at increased risk of more severe morning sickness:
Being a first-time mom
Morning sickness is often worse with first pregnancies. Subsequent pregnancies tend to have milder symptoms.
Having a history of nausea
Women prone to motion sickness or migraines seem more likely to experience severe morning sickness.
Being pregnant with multiples
Higher hCG levels in twin and triplet pregnancies increase odds of significant vomiting.
Having a female fetus
Some research indicates carrying a female baby leads to higher hCG levels and increased nausea/vomiting severity.
Obesity
Obesity appears associated with more hyperemesis gravidarum, the most severe form of morning sickness. The reasons are unclear.
Younger or older maternal age
The risk of excessive vomiting is greater at the extremes of reproductive age. Teen moms and women over 35 may be most affected.
When to see your doctor
Contact your doctor if you experience:
- Vomiting more than 3-4 times per day
- Inability to keep down food or liquids for 24 hours
- Weight loss of more than 5% of body weight
- Signs of dehydration like dizziness, increased heart rate, dark urine
- Persistent vomiting after week 14
These can be signs of a more serious condition like hyperemesis gravidarum and may require IV fluids or medication.
Treatments for morning sickness
Lifestyle adjustments like eating smaller meals, avoiding triggers, and resting often ease morning sickness. Other remedies include:
Vitamin B6
Studies show vitamin B6 supplements reduce nausea and vomiting in pregnancy. Doses of 25-50 mg up to 3 times per day appear effective and safe.
Doxylamine
This antihistamine reduces nausea and vomiting. It’s often combined with vitamin B6 and sold as Diclegis or Bonjesta.
Ginger
Ginger may reduce nausea and vomiting by 25%. Capsules, tea, and ginger ale can help. Choose products standardized for gingerol levels.
Acupressure
Wrist bands that apply pressure to the P6 acupressure point on the inner forearm may curb nausea. They’re drug-free and inexpensive.
Prescription medication
For severe cases unresponsive to natural remedies, prescription meds like ondansetron or promethazine may be used short-term.
When does morning sickness go away?
For 50-90% of women, morning sickness resolves by weeks 14-16 of pregnancy. But around 10% continue having symptoms after week 20. A small number battle nausea and vomiting for the full 40 weeks. While difficult to cope with, morning sickness lasting the entire pregnancy does not typically harm mom or baby. Staying hydrated, well-nourished, and rested is key. If symptoms are severe and persistent, medication may help provide relief.
Conclusion
Morning sickness like nausea and vomiting affects most women during early pregnancy. While the exact cause is uncertain, rapidly rising hCG and estrogen levels play a central role. A sensitive stomach, nose, and inner ear contribute. Vomiting results from direct stimulation of the vomiting center in the brain by pregnancy hormones and other factors. While uncomfortable, morning sickness is viewed as beneficial overall and a normal part of a healthy pregnancy. Lifestyle adjustments and remedies like vitamin B6, ginger, and acupressure can provide relief in many cases. But if vomiting is excessive or preventing nutrition and hydration, promptly contacting your doctor is important.