Morning sickness, also known as nausea gravidarum, is that nauseous, fatigued feeling that has

been ruining days of pregnant women for all time. The term "morning sickness" is kind

of a cruel joke, since, if you've ever been around a pregnant lady or been a pregnant

lady, you know that the agony can strike any time of day or night or just linger. All the

time. It's not fun.

This nausea can be mild--similar to feeling sleep deprived, hungover, or like you were

stuck on the tilt-a-whirl all day--or it can be strong enough to cause vomiting. Which

I probably don't have to tell you is far less cute and funny as it's often portrayed in

rom-coms where the heroine daintily pukes into a wastebasket in front of her coworkers

and then suddenly feels fresh as a daisy.

For a small proportion of women, around one percent, these symptoms become so severe that

they may lead to weight loss, dehydration, a dangerous drop in blood acidity called alkalosis,

and hypokalemia or low blood potassium levels. This extreme morning sickness is called hyperemesis

gravidarum, and it can be very dangerous. Luckily, no matter how bad you may get it,

most women find their morning sickness starts to fade in the second trimester.

So, what causes this misery? Why wasn't nature satisfied with pregnancy causing just bloating

and backaches and constipation and weird facial skin discoloration?

Well, the short answer is that we... don't really know, but because this is science we're

talking about, there are, of course, several theories.

Many experts believe that those craptastic feelings are triggered by the truly insane

amount of hormonal changes pregnant women experience early on. Especially the increase

of human chorionic gonadotrophin, or HCG. HCG is produced by the developing embryo after

conception and later by the placenta. It's released to help the ovaries keep producing

the hormones necessary to sustain pregnancy.

In most normal pregnancies, the level of HCG in a woman's body doubles every two or three

days, getting higher and higher until it peaks around the third month. Some believe these

soaring hormone levels overstimulate the chemoreceptor trigger zone, or CTZ, the part of the brain

that controls the so-called "vomit reflex." And then, it's hello, Puke City.

But HCG is only one of several tricky hormones at work here. Some scientists suggest estrogen

levels may be partly to blame because they can be one hundred times higher during pregnancy

than they normally are. Although, so far, studies have found no correlation between

estrogen levels in pregnant women who experience morning sickness and those who don't.

And then there's progesterone, which also skyrockets during pregnancy in part to relax

the uterine muscles to prevent early childbirth, but this hormone also relaxes the stomach

and intestinal muscles, which may lead to extra stomach acid and acid reflux, which

could factor into morning sickness.

Hypoglycemia or low blood sugar caused by the energy drained from the growing placenta

may also play a role in the stomach upset, which is why doctors recommend pregnant women

eat lots of small meals throughout the day. Still others maintain the heightened sense

of smell associated with pregnancy may similarly make some mamas extra sensitive to unpleasant

smells.

Perhaps the most interesting theory, though, and it is just a theory, suggests that morning

sickness may actually be a useful evolutionary adaptation. The idea here is that easily triggered

nausea may help protect expectant mothers from eating the wrong thing and getting food

poisoning, thus protecting their babies from toxins.

When you're feeling crappy, you tend to look for foods that are naturally low risk for

contamination. Simple carbs, like crackers and rice and bread, tend to be far more appealing

to a queasy mom than meat and eggs and dairy, even certain vegetables, all of which can

spoil easily in ways that can be hard to detect. So perhaps the body is telling the mother

to stick to safer, blander foods to increase her child's chances for survival. And it so

happens that a developing baby's vulnerability to certain toxins peaks at the end of the

first trimester, which is also when morning sickness tends to ease up.

We may never know the exact causes of morning sickness, but the results are often painful

and plain, so make sure you're extra nice to all those pregnant ladies. They're traveling

a rough road.

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