Morning Sickness: What Causes Morning Sickness?

I am newly pregnant and feeling a bit nauseous. What causes morning sickness?


Peg Plumbo CNM

Peg Plumbo has been a certified nurse-midwife (CNM) since 1976. She has assisted at over 1,000 births and currently teaches in the... Read more

We don't really know what causes nausea in pregnancy. Some theories have to do with the hormone progesterone, which is the dominant hormone during pregnancy. It has a generalized "softening" effect on smooth muscle, which would include the stomach. Perhaps this effect was meant for the uterus to prevent preterm labor, but its effects are also generalized to many other organs. We know that the entire gastrointestinal system slows down and this is what causes constipation in pregnancy.

Another theory is that elevated levels of steroid hormones and hCG (human chorionic gonadotopin) may be involved. These hormones are secreted by the ovary and the newly implanting embryo. Several studies have suggested that pregnancies "complicated" by nausea have better outcomes (fewer miscarriages). So it may be that nausea is actually a good thing!

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