What causes nausea and vomiting during pregnancy?
No one knows for sure what causes nausea during pregnancy, but it's probably some combination of the many physical changes taking place in your body. Some possible causes include:
Human chorionic gonadotropin (hCG). This hormone rises rapidly during early pregnancy. No one knows how hCG contributes to nausea, but it's a prime suspect because the timing is right: Nausea tends to peak around the same time as levels of hCG. What's more, conditions in which women have higher levels of hCG, such as carrying multiples, are associated with higher rates of nausea and vomiting.
Estrogen. This hormone, which also rises rapidly in early pregnancy, is another suspect. (It's possible that other hormones play a role as well.)
An enhanced sense of smell and sensitivity to odors. It's not uncommon for a newly pregnant woman to feel overwhelmed by the smell of a bologna sandwich from four cubicles away, for example. Certain aromas instantly trigger the gag reflex. (Some researchers think this may be a result of higher levels of estrogen, but no one knows for sure.)
A sensitive stomach. Some women's gastrointestinal tracts are simply more sensitive to the changes of early pregnancy. Also, some research suggests that women with a stomach bacterium called Helicobacter pylori are more likely to have nausea and vomiting. Not all studies confirm this link, though.
Stress. Some researchers have proposed that certain women are psychologically predisposed to having nausea and vomiting during pregnancy as an abnormal response to stress. However, there's no conclusive evidence to support this theory. (Of course, if you're constantly nauseated or vomiting a lot, you certainly may begin to feel more stressed!)