Table 1: Pregnancy-Risk Categories
| Category | Definition |
|---|---|
| A | Controlled studies in women fail to demonstrate a risk to the fetus in the first trimester, and the possibility of fetal harm appears remote. | B | Either animal studies do not indicate a risk to the fetus and there are no controlled studies in pregnant women, or animal studies have indicated fetal risk, but controlled studies in pregnant women failed to demonstrate a risk. |
| C | Either animal studies indicate a fetal risk and there are no controlled studies in women, or there are no available studies in women or animals. | D | There is positive evidence of fetal risk, but there may be certain situations where the benefit might outweigh the risk (life-threatening or serious diseases where other drugs are ineffective or carry a greater risk). |
| X | There is definite fetal risk based on studies in animals or humans or based on human experience, and the risk clearly outweighs any benefit in pregnant women. |
The Cleveland Clinic Foundation;
Adapted from: Briggs GG, Freeman RK, Yaffe SJ.
Drugs in pregnancy and lactation. 5th ed. Baltimore: Williams & Wilkins;1998.