The Placenta

The placenta, which implants itself in the uterus soon after conception to form a way station between woman and fetus, was thought to provide seamless protection from harmful substances.  Medical historian Ann Dally traces this sanguine notion back to the attitudes of the late nineteenth century.  “The Victorian tendency to put woman on a pedestal led to the idealization of the womb as well as of the woman,” she writes, and to “a believe in the placenta as a perfect barrier against damanging influences.”  This conviction was still current in the 1950s, when Dally attended medical school; there she was taught that a toxin would affect the fetus only if it actually killed the mother.  Pregnant women were not counseled about the dangers of medications or alcohol, Dally notes, and new drugs were not thoroughly tested for their safety during pregnancy.

– How the Nine Months Before Birth Shape the Rest of Our Lives (2010) by Annie Murphy Paul; page 79

Today, we now know that once chemicals do cross the placenta, chemicals can affect fetuses more powerfully than adults, for several reasons:

1) The fetus is so small that, pound for pound, it receives a higher relative dose of the chemical than would a person who’s fully grown;

2) The fetus’s detoxification and immune systems are still immature, unable to clear drugs and other chemicals from its system as effectively as the body of an adult; and,

3) The fetus is developing so rapidly that even a small disruption induced by a chemical can have far-reaching effects.