Morning Sickness and the Risk of Miscarriage

pregnancy morning sickness
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Morning sickness also referred to as nausea and vomiting of pregnancy, is common and occurs in around 63 percent of pregnant women. 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 women who have morning sickness during the first trimester have a 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 women who experience little or no morning sickness go on to deliver full-term healthy babies, and some women who experience morning sickness have miscarriages. Let's talk about what the studies show, including the theory for why women may experience morning sickness 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 if having morning sickness had a relationship to miscarriage. Of these women (who had their pregnancies confirmed by a measurement of hCG), those who experienced morning sickness were between 50 and 75 percent less likely to have a miscarriage than those who did not experience nausea and vomiting of pregnancy.

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

Lack of Morning Sickness and Other Pregnancy Problems

In addition to an increased risk of miscarriage, women who do not have morning sickness 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 and most women who do not have morning sickness do not experience preterm labor or have infants who suffer intrauterine growth retardation.

Morning Sickness Is Not Always a Good Sign

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 many people who do not experience morning sickness go on to deliver healthy infants.

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.

A 2014 study found that women who experience morning sickness were more likely to experience pregnancy-induced hypertension and have low birth weight babies.

What Causes Morning Sickness?

We 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 the level of this peaks 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). It's also thought that foods with high levels of phytochemicals may be disliked by pregnant women as these strong tasting foods are more likely to be teratogenic (cause birth defects) than foods with low levels of phytochemicals such as corn.

What Should You Do If You Don't Have Morning Sickness?

If you don't have morning sickness or if your morning sickness has disappeared, don't panic. Nausea is not a prerequisite for having a healthy pregnancy—plenty of women never have morning sickness at all. If you are concerned about miscarriage, learn about the risk factors for miscarriage, some which can be prevented, but many which cannot.

In addition, having morning sickness does not guarantee you will not have a miscarriage; it's possible to miscarry even if you have noticeable pregnancy symptoms.

Sources:

Hinkle, S., Mumford, S., Grantz, K. et al. Association of Nausea and Vomiting during Pregnancy With Pregnancy Loss: A Secondary Analysis of a Randomized Clinical Trial. JAMA Internal Medicine. 2016. 176(11):1621-1627.

Koren, G., Madjunkova, S., and C. Maltepe. The Protective Effects of Nausea and Vomiting of Pregnancy Against Adverse Fetal Outcome—A Systematic Review. Reproductive Toxicology. 2014. 47:77-80.

Parker, S., Starr, J., Collett, B., Speltz, M., and M. Werler. Nausea and Vomiting During Pregnancy and Neurodevelopmental Outcomes in Offspring. Paediatric and Perinatal Epidemiology. 2014. 28(6):527-35.

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