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“Morning” sickness, or pregnancy sickness, refers to the experience of nausea, vomiting, and aversions to certain foods during the first trimester of pregnancy. Around two-thirds of women experience symptoms of morning sickness and mild weight loss early in pregnancy. Around 1% of women may also experience hyperemesis gravidarum, a more severe form of pregnancy sickness that results in severe nausea, profuse vomiting, and often, dehydration.
Very little data exist that cite pregnancy-sickness-like illness and emesis in early pregnancy in non-human primates, though reports of reduced food intake and weight loss have been documented in a single captive chimpanzee. Rhesus monkeys and dogs have also been observed to experience a decrease in appetite, often used as an indicator of early pregnancy in laboratory colonies. Vomiting and food aversions have not been reported. Morning sickness in non-humans may difficult to study due to difficulties in detecting early pregnancy, particularly in the wild.
Data across cultures have shown that the incidence of pregnancy sickness is much lower in societies where consumption of meat is relatively low, and where cereals and grains are primary dietary staples.
Women who experience pregnancy sickness are less likely to miscarry than women who do not show symptoms. Pregnancy sickness may play an adaptive role in protecting expectant mothers and their offspring from harmful toxins consumed in the diet. Many food aversions have been reported, but most commonly involved caffeinated or alcoholic beverages, strongly-flavored vegetables, and animal products. Pregnant women additionally show a heightened disgust response in the first trimester, particularly with reference to food and illness related questions designed to provoke disgust responses.
Pregnancy sickness may also serve to aid in embryogenesis and fetal development by encouraging maternal lipolysis, whereby fat stores are broken down to provide energy for mother and offspring, and producing ketones, an optimal fuel source for the developing brain. Further, the breakdown of lean maternal tissues, in addition to mechanisms that conserve maternal urea production, lead to dramatically increased nitrogen levels in maternal circulation, indicated in isotopic analyses of hair samples. Increased nitrogen in maternal circulation from the breakdown of maternal bodily tissues due to morning sickness likely contributes to the generation of structural proteins important for building fetal bodily tissues.
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Elevated disgust sensitivity in the first trimester of pregnancy: Evidence supporting the compensatory prophylaxis hypothesis, , Evolution and Human Behavior, 07/2005, Volume 26, Issue 4, p.344 - 351, (2005)
Nitrogen balance and delta15N: why you're not what you eat during nutritional stress., , Rapid Commun Mass Spectrom, Volume 19, Issue 18, p.2497-506, (2005)
Morning sickness: a mechanism for protecting mother and embryo., , Q Rev Biol, 06/2000, Volume 75, Issue 2, p.113-48, (2000)
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