The Facts
Many pregnant women (about 70% to 85%) experience a period of nausea and vomiting. In the vast majority of cases, it's unpleasant but not dangerous. About 4 in 1,000 expectant mothers will vomit so severely that they lose weight and become dehydrated, requiring hospital treatment. This severe form of morning sickness is called hyperemesis gravidarum. Although this condition could be life-threatening if left untreated, it can be remedied by treatment during a brief hospital stay.
When a woman has morning sickness, it can be severe enough that she may have difficulty working. Although called "morning sickness," the nausea and vomiting may occur at any time of day.
Causes
While the exact causes of morning sickness aren't known, it's probably linked
to pregnancy hormones. Women who suffer morning sickness tend to have higher
levels of these hormones than those who don't. Very probably, it's an ancient
mechanism for protecting the fetus from poisons. With the enormously rich and
varied diet we eat today compared to our ancestors, it's no surprise that such
a protective system could become a bit confused and start rejecting all sorts
of healthy food.
One piece of evidence for this idea can be found in research showing that women
who suffer from vomiting during pregnancy actually have lower rates of miscarriage
than women who don't. Research shows higher levels of two hormones (thyroxine and human chorionic
gonadotropin) in women with morning sickness. Women who suffer nausea from
the birth control pill are more likely to develop morning sickness during pregnancy.
