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  • [Intro]

  • 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.

  • Thanks for watching this SciShow Dose, and if you'd like to help us keep exploring the

  • world, just go to to find out how you can become a supporter, and

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B2 中高級

晨吐的原因是什麼? (What Causes Morning Sickness?)

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    稲葉白兎 發佈於 2021 年 01 月 14 日