A common misconception about evolution is that it always results in progress, and species and organisms become perfectly adapted to their environments and circumstances over time. The reality is that natural selection is perfectly content with good-enough, and is quite hospitable to maintaining traits that are deeply flawed.
I’ve long imagined that at least some of the difficulties surrounding conception and pregnancy fall under this category; the reproductive process for humans works, but it is far from ideal. The act of making, gestating and birthing babies is grueling, and subjects women to a considerable amount of discomfort. One of the biggest struggles comes during the first trimester, when the majority of women experience extreme exhaustion and nausea. I’m currently nearing the end of this period myself, and have spent much of the past two months wondering if, as some have suggested, there is an adaptive purpose to feeling like crap.
Now new research from the National Institutes of Health suggests that there is something protective about morning sickness. Recently published in JAMA Internal Medicine, the study looked at the correlation between nausea and miscarriage rates among nearly 800 women and found that those who experienced the symptom had a 50 to 75 percent lower risk of losing the pregnancy compared to those who didn’t.
The researchers relied on data collected for another study which looked at the effect of taking aspirin on gestation and reproduction. All of the women who participated in the study had previously experienced a miscarriage.
As part of the original study, the women who got pregnant kept a daily diary during the first trimester in which they recorded their symptoms, and they filled out monthly questionnaires through their 36th week of pregnancy. This record-keeping sets the morning-sickness study apart from most previous studies on nausea and pregnancy loss, which relied on women’s recollection of symptoms later in the pregnancy or after the miscarriage. (Our memories are never quite as accurate as we’d like them to be, and neither are studies built around them.) Also, unlike most previous studies, the researchers controlled for other potential risk factors for miscarriage, including history of repeated pregnancy loss, stress, cigarette and alcohol use, and chromosomal abnormalities. (However, the participants were disproportionately young, white, and married.)
Scientists aren’t sure why women experience morning sickness. Some have theorized that the symptoms are an adaptive mechanism that pushes women to avoid potentially toxic foods and substances. The new study did not examine this theory in terms of food intake, but it did look at whether morning sickness deterred women from potentially harmful substances like alcohol and cigarettes. They decided that “the [pregnancy protecting] mechanism is likely not through avoidance of such substances.”
Others believe that nausea is the result of rising human chorionic gonadotropin, or hCG, levels. (This is a hormone unique to pregnancy, the one that makes an extra line or happy face appear on a pregnancy test.) Levels of this hormone rise throughout the first trimester, after which they level off or decline. The study did not test the relationship between hormones and morning sickness.
The authors of the study write that their findings “may provide reassurance to women experiencing these difficult symptoms in pregnancy.” As someone just exiting the throes of the first trimester, I am indeed feeling some reassurance, but not enough to counter my frustration over feeling terrible for the past two months. In an editorial published alongside the study in JAMA, OB/GYN Dr. Siripanth Nippita and scientist Laura Dodge, both from Beth Israel Deaconess Medical Center in Boston, praise the findings, but also warn against using them as a way to tell women to just deal with it.* “As common as nausea and vomiting are in the first trimester of pregnancy, researchers and clinicians should be cautious about deeming it to have a protective effect against pregnancy loss,” they write. Also, women “should not be discouraged from seeking treatment for a condition that can have a considerable negative effect on their quality of life.”
As beneficial as morning sickness may be, please don’t ever tell a pregnant woman she is lucky to be experiencing it.
*Correction, Sept. 28, 2016: This post originally misidentified Beth Israel Deaconess Medical Center as Israel Deaconess Medical Center.