Answer 1:
The quick answer to this question is that statistically morning sickness reduces the likelihood of miscarriage, pre-term birth, low birthweight and perinatal death. More interesting is the question of how this advantage is conferred. No one really knows, although several theories have been advanced.
The traditional hypothesis is that nausea and vomiting make pregnant women avoid foodstuffs containing chemicals likely to harm the foetus during the critical period of organ formation.
There is a variety of evidence to support this: symptoms peak when embryonic organogenesis is most susceptible to chemical disruption, between 6 and 18 weeks into pregnancy; women who experience morning sickness are less likely to miscarry than women who do not; women who vomit suffer fewer miscarriages than those who experience nausea alone; and many pregnant women have aversions to alcoholic and caffeinated drinks and strong-tasting vegetables, especially during the first trimester.
However, because it appears that the greatest aversions are to meat, fish, poultry and eggs, the theory now goes that the purpose is to reduce exposure to potential food-borne pathogens. This may be because the immune system is weakened during this period of pregnancy.
An interesting alternative hypothesis put forward recently is that starving the mother during the first trimester causes a corresponding increase in the size of the placenta. This ensures better nutrition for the foetus for the rest of the pregnancy, reducing the risk of miscarriage.
This has been known to sheep farmers for some time. Apparently, many of them ensure that their ewes are mated while feeding on poor pasture, where they remain for the first half of the pregnancy before being moved to better pasture for the remainder. The result is larger lambs, presumably because the starvation during early pregnancy results in a larger placenta.
However, one study of this in humans which failed to find any significant link between vomiting in early pregnancy and higher birthweight. On the other hand, vomiting in late pregnancy was found to lead to significantly reduced birthweight.
Answer 2:
Margie Profet, a physician has written extensively on morning sickness as an evolutionary adaptation. She argues that food aversions and vomiting in early pregnancy are a way of ensuring that embryos are protected from toxins that could harm them while the limbs and major organ systems are forming.
There is, however, a cost associated with pregnancy sickness: the loss of important nutrients. It is presumably for this reason that morning sickness stops once the embryo has developed into a foetus and is less vulnerable to toxins. One recent study found that morning sickness is likely to harm the foetus if the mother already suffers from poor nutrition. But for well-nourished women, the adaptive view of morning sickness implies that they should be wary of treatment that eliminate symptoms.
More research is needed into morning sickness in other animals, but most mammals and other creatures already display an innate or learned aversion to potentially harmful foods. Some mammals show physiological changes during pregnancy that heighten sensitivity to toxins. But Profet points out that morning sickness is likely to evolve in creatures that experiment, eating a variety of foods.
Women can experience dangerous amounts of vomiting during pregnancy, and should always seek medical advice. But in general they should look upon morning sickness not as an affliction but as a mechanism designed to protect the embryo.
Published in The Hindu on Jan 17, 2002.
Published in The Hindu on Jan 17, 2002.
