A theory on the biological function of what is commonly known as "morning sickness" is being presented by two biologists from Cornell University. The "embryo-protection hypothesis" reasons that the nausea and vomiting experienced to some degree by two-thirds of pregnant women, serves a beneficial function and is Mother Nature's way of protecting mothers and fetuses from food-borne illness and also shields the fetus from chemicals that can defects and deformities.

The researchers examined the outcomes of thousands of successful and unsuccessful pregnancies and came up with some startling observations:

• Women who experience morning sickness are significantly less likely to miscarry.
• Women who vomit are less likely to miscarry than those who only get nauseous are.
• Morning sickness usually peaks precisely at the time in development when the embryo is most susceptible to chemical disruption.
• The strongest aversions were to meats, fish, poultry, and eggs, which were all more likely to carry harmful microorganisms and parasites prior to modern technology, such as refrigeration.

The researchers state that attempting to alleviate the symptoms of normal morning sickness will not improve the outcome of the pregnancy and could have the exact opposite effect if potentially dangerous foods are not avoided. Additionally, women should not be encouraged to eat anything that they have an aversion to during pregnancy.

"In other words, listen to your body," said one of the researchers.

The Quarterly Review of Biology 2000; 75: 113-148