When a pregnant woman takes medication, both she and the unborn child are exposed to the drug.

The risks of adverse effects, for the mother and for the child, especially the risk of birth defects linked to medications taken during pregnancy, are poorly known overall. The available studies, in humans and in animals, are far from sufficient.

The principal known risks differ according to the stage of fetal development: embryo formation during the first trimester, organ development during the second and third trimesters, and the time near birth.

Until the 12th day after conception, it appears that the mother-fetus exchanges are still modest, and the risk to the embryo is considered to be small. The period from the 12th day to the 56th day of the pregnancy is the period when the risk of morphological damage is the greatest. Drug-induced disruptions of embryonic formation are most often attributed to the drug’s molecular structure, which interferes with the chemical messages governing organ formation. The consequences for the unborn child are morphological, anatomical abnormalities, most often detected during the morphological ultrasound examination in the fifth month.

In the second and third trimesters of pregnancy, the consequences for the fetus are most often a function of the drug’s pharmacodynamic properties, which are known and therefore easier to predict: failure of an organ to mature, functional disorders, developmental disorders, etc. At the end of pregnancy, drugs can interfere with labour, or can affect the newborn, which may experience the adverse effects for several days or weeks.

All in all, the effect of medications, including plant-based remedies, on the unborn child are poorly known and little studied.

©Prescrire 1 August 2013

Source: "Femmes enceintes et médicaments" Rev Prescrire 2013 ; 33 (358).