Morning sickness protects embryo?

MORNING SICKNESS PROTECTS EMBRYO?

"[W]omen who experience morning sickness are significantly less likely to
miscarry than women who do not..."
--Flaxman and Sherman [2000]

INTERESTINGLY: Flaxman and Sherman [2000] reported that in seven
"traditional" societies, morning sickness has "never been observed"...

Q Rev Biol. 2000 Jun;75(2):113-48. PubMed abstract

Morning sickness: a mechanism for protecting mother and embryo.

Flaxman SM, Sherman PW.

Department of Neurobiology and Behavior, Cornell University, Ithaca, New
York 14853, USA.

Approximately two-thirds of women experience nausea or vomiting during the
first trimester of pregnancy. These symptoms are commonly known as morning
sickness. Hook (1976) and Profet (1988) hypothesized that morning sickness
protects the embryo by causing pregnant women to physically expel and
subsequently avoid foods that contain teratogenic and abortifacient
chemicals, especially toxic chemicals in strong-tasting vegetables,
caffeinated beverages and alcohol. We examined this hypothesis by
comprehensively reviewing the relevant medical, psychological and
anthropological literature. In its support, (i) symptoms peak when embryonic
organogenesis is most susceptible to chemical disruption (weeks 6-18), (ii)
women who experience morning sickness are significantly less likely to
miscarry than women who do not (9 of 9 studies), (iii) women who vomit
suffer fewer miscarriages than those who experience nausea alone, and (iv)
many pregnant women have aversions to alcoholic and nonalcoholic (mostly
caffeinated) beverages and strong-tasting vegetables, especially during the
first trimester. Surprisingly, however, the greatest aversions are to meats,
fish, poultry, and eggs. A cross-cultural analysis using the Human Relations
Area Files revealed 20 traditional societies in which morning sickness has
been observed and seven in which it has never been observed. The latter were
significantly less likely to have animal products as dietary staples and
significantly more likely to have only plants (primarily corn) as staples
than the 20 societies in which morning sickness occurred. Animal products
may be dangerous to pregnant women and their embryos because they often
contain parasites and pathogens, especially when stored at room temperatures
in warm climates. Avoiding foodborne microorganisms is particularly
important to pregnant women because they are immunosuppressed, presumably to
reduce the chances of rejecting tissues of their own offspring (Haig 1993).
As a result, pregnant women are more vulnerable to serious, often deadly
infections. We hypothesize that morning sickness causes women to avoid foods
that might be dangerous to themselves or their embryos, especially foods
that, prior to widespread refrigeration, were likely to be heavily laden
with microorganisms and their toxins. The alternative hypotheses that
morning sickness is (i) an epiphenomenon of mother-offspring genetic
conflict or hormones associated with viable pregnancies, or (ii) an
indicator to potential sexual partners and kin that the woman is pregnant,
resulting in reduced sexual behavior and increased nepotistic aid, were not
well supported. Available data are most consistent with the hypothesis that
morning sickness serves an adaptive, prophylactic function.

END Flaxman and Sherman PubMed abstract

Todd