Taking drugs during pregnancy. How safe are the unsafe?

I prescribed misoprostol to one of my patients with a peptic ulcer. When she found out she was pregnant while on the drug, both she and, admittedly, I were very scared to learn that the drug is teratogenic in that it causes Möbius syndrome. How great is the risk?

Very small. Although women who use misoprostol during the first trimester have a 30-fold higher risk of having babies with Möbius syndrome, the malformation is so rare that, even if you see 1000 women who took misoprostol during embryogenesis, you might not see a single child with the syndrome. It is crucial to explain the size of the risk; otherwise women tend to believe the risk is huge even when, in fact, it is hardly measurable.