Morning sickness linked to lower risk of pregnancy loss

In the largest and most in-depth study of its type, morning sickness is found to have a protective effect on the unborn child. Despite its unpleasant nature, morning sickness appears to be a component of a healthy pregnancy.
[Pregnant woman's belly]
New research into morning sickness shows the benefits behind the discomfort.

Morning sickness is incredibly common in early pregnancy.

It is referred to as “morning” sickness because it tends to come on during the morning hours and steadily improve over the course of the day.

In reality, it can strike at any point in the day and is a unanimously unpleasant feeling.

Around 50 percent of pregnant women simply feel nauseous, but roughly half will also experience vomiting. A rare few, perhaps 1 in 100, are so sick that they require hospital treatment.

Generally, the sickness eases after the fourth month of pregnancy, but – for some mothers – it can continue throughout the entire pregnancy.

The reasons behind morning sickness have been debated over the years; hormonal changes in the first 12 weeks are thought to be at least partially to blame. Fluctuations in estrogen, progesterone, and human chorionic gonadotropin may all be involved.

Why does morning sickness occur?

Why morning sickness occurs is also up for debate. A common theory is that it evolved as a mechanism to steer pregnant women away from foods that might carry risks. Morning sickness tends to peak at around 3 months, which is the time when a fetus is most vulnerable to toxins.

In general, morning sickness is viewed as a sign of a healthy pregnancy. However, to date, studies investigating whether this rings true have not had a sufficient level of detail. As Stefanie N. Hinkle, Ph.D, a staff scientist in the National Institutes of Health’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Epidemiology Branch and first author of the present study, says: “there wasn’t a lot of high-quality evidence to support this belief.”

A study reopening this question was recently completed by the NICHD. Published in JAMA Internal Medicine, the experiment set out to test this theory in more depth: does the presence of morning sickness signal a reduced risk of pregnancy loss?

Hinkle and her team used data from the Effects of Aspirin in Gestation and Reproduction (EAGeR) trial. EAGer was designed to test the effects of low-dose aspirin on women who had experienced one or two pregnancy losses in the past.

The participants each kept a diary in which they noted feelings of nausea between weeks 2 and 8 of pregnancy. They also responded to a monthly questionnaire on their symptoms up until the 36th week of pregnancy.

The protective nature of morning sickness

Previous studies investigating the protective effects of morning sickness had relied on women’s recollections of sickness symptoms much later in pregnancy, or after they had lost a pregnancy. This was the first study to track morning sickness in real time.

The EAGer trial consisted of 797 pregnant women. In total, 188 pregnancies ended in loss. By the 8th week, 57.3 percent of women reported having experienced nausea, and 26.6 percent reported experiencing nausea and vomiting.

Analysis of the data showed that the women who experienced morning sickness were 50-75 percent less likely to experience pregnancy loss than those who had neither vomiting nor nausea.

“Our study evaluates symptoms from the earliest weeks of pregnancy, immediately after conception, and confirms that there is a protective association between nausea and vomiting and a lower risk of pregnancy loss.”

Stefanie N. Hinkle, Ph.D.

The results demonstrate that morning sickness appears to be a sign of a healthy pregnancy and perhaps has certain protective qualities. Although this study is of unparalleled size and quality, more work still needs to be done.

The participants used in the current study had all experienced at east one failed pregnancy in the past, making them a certain subset of the population. Also, the question of exactly how morning sickness reduces risk cannot be ascertained from the present study.

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