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Morning sickness, also called nausea and vomiting of pregnancy (NVP), nausea gravidarum, emesis gravidarum, and pregnancy sickness, is a pregnancy discomfort that affects more than half of all pregnant women. Symptoms may be present early in the morning and reduce as the day progresses. However, in spite of its common name, nausea and vomiting of pregnancy can occur at any time during the day. For most women the sickness ends around the 12th week of pregnancy (the end of the first trimester). Related to increased estrogen levels, a similar form of nausea is also seen in some women who use hormonal contraception or hormone replacement therapy. The nausea can be mild or induce actual vomiting. In more severe cases, vomiting may cause dehydration, weight loss, high blood pH, and a low level of potassium in the blood. This condition is known as hyperemesis gravidarum and occurs in about 1% of all pregnancies. Nausea and vomiting can be one of the first signs of pregnancy and usually begin around the 6th week of pregnancy (counting gestational age from 14 days before conception). ==Causes== Proximate causes of pregnancy sickness include: * Excess salivation during the first trimester, that is often bitter tasting (ptyalism), is then ingested during the mother's sleep. * An increase in the circulating level of the hormone estrogen. However, there is no consistent evidence of differences in estrogen levels and levels of bilirubin between women that experience sickness and those that do not. * Low blood sugar due to the placenta's draining energy from the mother, though studies have not confirmed this except for in Type I diabetic expectant mothers. * An increase in progesterone relaxes the muscles in the uterus, which prevents early childbirth, but may also relax the stomach and intestines, leading to excess stomach acids and gastroesophageal reflux disease (GERD). * An increase in human chorionic gonadotropin. It is probably not the human chorionic gonadotropin itself that causes the nausea. More likely, it is the human chorionic gonadotropin stimulating the maternal ovaries to secrete estrogen, which in turn causes the nausea. * An increase in sensitivity to odors, which overstimulates normal nausea triggers. * An increase in bilirubin levels due to increased liver enzymes. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「morning sickness」の詳細全文を読む スポンサード リンク
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