Morning Sickness and the Risk of Miscarriage

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Morning sickness, also referred to as nausea and vomiting of pregnancy, is common and occurs in 50% to 80% of pregnancies. Morning sickness is usually the worst during the first trimester, with symptoms resolving early in the second trimester. There have been numerous studies showing that people who have morning sickness during the first trimester have lower odds of miscarriage and other negative pregnancy outcomes. But what does that mean?

While morning sickness, in general, is associated with better pregnancy outcomes, it's important to keep in mind that this is a statistical phenomenon. Many pregnant people who experience little or no morning sickness go on to deliver full-term healthy babies, and some who experience morning sickness have miscarriages. Let's talk about what the studies show, including the theory for why morning sickness can occur in the first place.

Morning Sickness and Miscarriage Risk

A 2016 study looked at women who had already had one or two miscarriages to see whether having morning sickness had a relationship to miscarriage.

Of these women (who had their pregnancies confirmed by measuring hCG levels), those who experienced morning sickness were between 50% and 75% less likely to have a miscarriage than those who did not experience nausea and vomiting of pregnancy.

In addition, women who have nausea and vomiting, are less likely to have a miscarriage than those who have nausea alone.

Other Pregnancy Problems

In addition to an increased risk of miscarriage, people who do not have morning sickness during pregnancy also appear to have an increased risk of preterm delivery as well as pregnancies complicated by intrauterine growth retardation. Again, however, this is a statistical finding; most pregnant people who do not have morning sickness do not experience preterm labor or have infants who experience intrauterine growth retardation.

Other Risks With Morning Sickness

Hearing about the statistics related to a lack of morning sickness and miscarriage may make you feel anxious, so it's important to again note that people who do not experience morning sickness during pregnancy go on to deliver healthy infants. Also, there are at least seven traditional societies known for a lack of morning sickness among pregnant people.

On the other hand, severe morning sickness can be associated with poor weight gain, and poor weight gain is, in turn, associated with a number of problems such as low birth weight babies.

Causes

Experts don't exactly know what causes morning sickness. It's thought that in addition to physiological causes, there may be psychological, genetic, and cultural factors as well.

Morning sickness may be related to the secretion of hCG as levels peak at around 12 weeks gestation, the same time at which morning sickness is at its worst.

The exact reason for the link between morning sickness and miscarriage risk is not known, but one possible explanation is that non-viable pregnancies, such as those affected by chromosomal abnormalities, have lower hCG levels and this might lead to fewer pregnancy symptoms.

Purpose of Morning Sickness

After hearing stories about morning sickness, you may be wondering what purpose morning sickness could possibly have. As we learn more about the human body, we are learning more about how intricate and amazingly we are designed.

Many functions that we once viewed as problems or redundant and leftover from evolution now appear to have a purpose. Just as there is a purpose for tonsils and an appendix, it's thought by evolutionary biologists that morning sickness has a purpose as well.

Morning sickness very closely mirrors the period of time when the development of the fetus is at the greatest risk of damage; the time when the most significant changes in fetal development are occurring.

It's thought that morning sickness may restrict the intake of nutrients which may cause foodborne illness or mutations in the developing cells.

The most common food aversions tend to be towards meats, fish, poultry, and eggs, the foods the are most likely to be a source of harmful bacteria and parasites, especially before refrigeration was available.

A Word From Verywell

Just as having morning sickness does not guarantee you will not have a miscarriage, not experiencing morning sickness doesn't mean that you will miscarry. If you are pregnant but are not experiencing morning sickness, or if your morning sickness has disappeared, don't panic. Nausea is not a prerequisite for having a healthy pregnancy—plenty of pregnant people never have morning sickness at all. If you are concerned about miscarriage, learn about the risk factors for miscarriage, some of which can be prevented, but many of which cannot.

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