WHEN a pregnant woman takes a drug, she risks spontaneous abortion or stillbirth. If her infant survives, it may suffer from effects ranging from temporary irritability to seizure or occasional physical birth defects.
Which condition occurs depends on both the type of drug and the amount that the fetus absorbs, according to Hazel Szeto, MD, Cornell University Medical Center, New York City. The amount of drug absorbed, in turn, depends on its lipid solubility, she says. A less lipid-soluble substance, like morphine, will not pass as easily through the placenta and will therefore not cause as great adverse effects as a more lipidsoluble substance, such as methadone.
Fetus Has Defenses
But the fetus is not helpless against highly lipid-soluble drugs, Szeto says. It can defend itself. Szeto found, in a study on the effects of opiates on pregnant ewes, that the fetus clears drugs not only by renal elimination and