Medication safety in pregnancy

What it is

Before a drug is given to a woman in her reproductive years, ask about the menstrual history and about whether she could be pregnant, because several drugs in wide use are teratogenic. Three lists matter: the drugs that must not be given, the ones that may, and the counseling a teratogenic drug needs before the first dose. Drug therapy in pregnancy cannot and should not be avoided; the rule is that medication should only be used if the expected benefits, usually to the mother, are greater than the potential risks, usually to the fetus, because many drugs cross the placenta and expose the developing embryo and fetus to their pharmacologic and teratogenic effects. Try to avoid first trimester use, use drugs that have been used extensively in pregnancy rather than new ones, be prepared to adjust doses as pregnancy progresses and drug handling is altered, use the minimum dose required to obtain the desired effect, and absence of data does not imply safety. Two systems of pregnancy risk category are set out side by side, the Swedish FASS and the Australian ADEC. Category A is a drug taken by a large number of pregnant women without evidence of fetal harm; B rests on animal data and is divided into B1, where animal experiments have shown no increased fetal damage, B2, where animal studies are insufficient, and B3, where animal studies found increased fetal damage of uncertain significance in humans; C and D are the two rows where the two systems part in their criteria, the rows from A to B3 being marked in ADEC as the same as FASS. C in FASS is drugs that by their pharmacologic effects have caused, or must be suspected of causing, disturbances in the reproductive process that may involve risk to the fetus without being directly teratogenic, and in ADEC it is drugs that have caused, or may be suspected of causing, harmful effects on the human fetus or neonate without causing malformations, effects that may be reversible. D in FASS is animal and human data indicating an increased incidence of fetal malformations or other permanent damage in humans, and in ADEC it is drugs that have caused, are suspected to have caused, or may be expected to cause an increased incidence of human fetal malformations or irreversible damage; and X, which exists in ADEC only, is a drug with so high a risk of permanent damage that it should not be used in pregnancy at all.