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What Causes Morning Sickness?

By J. Beam
Updated: Mar 03, 2024

Morning sickness is the standard term applied to nausea and vomiting during pregnancy. Though it’s called morning sickness and many women find the nausea and vomiting are worse in the morning, it can occur at any time of the day. Morning sickness usually disappears at the end of the first trimester, giving way to indigestion and heartburn during the third trimester when the uterus has expanded to accommodate the growing fetus and puts pressure on the upper digestive track.

The physical causes of morning sickness are not clearly known, but it is clearly linked to the hormonal and physical changes that a woman’s body undergoes with pregnancy. One theory is that the increase in the hormone human chorionic gonadotropin (hCG) is the primary cause of morning sickness. Another possible cause of morning sickness is heightened sensitivity to odors. An odor that may not have been offensive prior to pregnancy can suddenly become nauseating, triggering the gag reflex. This may also be linked to an increase in hormones, specifically estrogen, but is still unknown.

A woman’s gastrointestinal system might react strangely to the changes that occur during pregnancy. Odds are that morning sickness is caused by any combination of increased hormone levels and physical changes. Some studies indicate that morning sickness is a sign of a healthy pregnancy and lowers the risk of complications later.

Nearly three-quarters of pregnant women have morning sickness at some point and to some degree during their pregnancy. It is more common in first pregnancies, but can also happen in subsequent pregnancies. The most common treatment for morning sickness is to grin and bear it.

It may help to eliminate foods that trigger nausea or are spicy or fatty. Eating a bland diet helps many women get through the morning sickness period. You can also try eating small portions more frequently and avoiding large meals all together.

If you experience morning sickness without relief, you may want to talk to your doctor about switching prenatal vitamins or about taking vitamin B6. Though the effectiveness of vitamin B6 on morning sickness has not been proven, taking it has seemed to help some sufferers. Talk to your doctor before you begin taking any vitamins or medications during pregnancy.

If you suffer from morning sickness so severely that it impacts your ability to eat or poses a risk for dehydration, you may have a more serious condition that can affect your pregnancy and your baby. Severe or excessive vomiting during pregnancy must be addressed by a physician. If you are newly pregnant and do not have a doctor, but are experiencing severe morning sickness, see your family physician or visit the emergency room. Dehydration during pregnancy can be serious.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
By anon111807 — On Sep 18, 2010

I've read that morning sickness is a defense mechanism to protect the fetus against toxins in certain foods. Is that correct? If so, then maybe it is counter-productive to take anti-nausea meds.

By anon72158 — On Mar 22, 2010

This sounds fine in theory, though i doubt seriously that morning sickness is due to smells. This is especially so, since some women can experience morning sickness through the night. If morning sickness can be related to hormones and physical changes which lead to heartburn etc., then could a remedy for morning sickness indeed be something as simple as gaviscon?

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