From the FDA Drug Label
Mifepristone is contraindicated in pregnancy because the use of mifepristone results in pregnancy loss. There are no data that assess the risk of birth defects in women exposed to mifepristone during pregnancy Available data limited to exposure following a single dose of mifepristone during pregnancy showed a higher rate of major birth defects compared to the general population comparator In a prospective study in France of 46 pregnancies exposed to a single dose of mifepristone alone and 59 pregnancies exposed to a single dose of mifepristone and misoprostol, the overall major birth defect rate (4%) was greater than the general population background rate of 2 to 3% (2 birth defects in each group). Animal Data Reproductive studies were performed in mice, rats and rabbits at doses of 0. 25 to 4. 0 mg/kg (less than human exposure at the maximum clinical dose, based on body surface area). Because of the anti-progestational activity of mifepristone, fetal losses were much higher than in control animals. Skull deformities were detected in rabbit studies at less than human exposure, although mifepristone did not cause any adverse developmental effects in rats or mice during organogenesis
The effects of mifepristone (RU-486) exposure on the neonate are not well understood, but available data suggest a potential increased risk of major birth defects.
- The overall major birth defect rate was greater than the general population background rate.
- Skull deformities were detected in rabbit studies.
- There are no data on long term exposure to mifepristone in pregnancy.
- The estimated risk of fetal loss is elevated in patients with active Cushing's syndrome.
- Mifepristone is present in human milk, but there are no data on the amount of mifepristone in human milk, the effects on the breastfed infant, or the effects on milk production during long term use of mifepristone 1
- Repeated doses of mifepristone to neonatal rats resulted in potentially adverse fertility effects, including oviduct and ovary malformations in females, delayed male puberty, deficient male sexual behavior, reduced testicular size, and lowered ejaculation frequency 1
From the Research
Mifepristone exposure has minimal effects on neonates when used for pregnancy termination or medical management of miscarriage, and current evidence does not suggest significant harmful effects on the developing fetus or resulting neonate. If a pregnancy continues after mifepristone exposure and the woman decides to continue the pregnancy, the most recent and highest quality study, a systematic review published in 2024 2, found that mifepristone is not implicated as a teratogen. Mifepristone is a progesterone receptor antagonist that blocks the action of progesterone, which is essential for maintaining pregnancy. When used in early pregnancy (typically before 10 weeks), it is usually followed by misoprostol to complete the termination process. The half-life of mifepristone is approximately 18-25 hours, meaning it is largely cleared from the maternal system within a few days. If a pregnancy continues despite mifepristone exposure, the ongoing production of progesterone by the placenta would likely overcome the temporary blocking effect of the medication.
Some key points to consider:
- The study published in 2024 2 is the most recent and highest quality study, and its findings should be given the most weight.
- While theoretical concerns exist about potential developmental effects due to the brief disruption of progesterone signaling, limited follow-up studies of continuing pregnancies after failed mifepristone administration have not demonstrated consistent patterns of congenital anomalies or developmental issues in exposed neonates.
- Another study published in 2013 3 found that the rate of major congenital malformations after first-trimester exposure to mifepristone is only slightly higher than the expected 2-3% rate in the general population.
- However, data remains limited, and any pregnancy that continues after mifepristone exposure should receive standard prenatal care with appropriate monitoring.
- It is also important to note that misoprostol, which is often used in combination with mifepristone, may have its own risks and side effects, as reported in a case study published in 2008 4.
In terms of clinical management, any pregnancy that continues after mifepristone exposure should receive standard prenatal care with appropriate monitoring, as recommended by the most recent and highest quality study 2. This includes regular ultrasound examinations and monitoring of fetal development to detect any potential anomalies or issues. Additionally, women who have been exposed to mifepristone and are continuing their pregnancy should be informed of the potential risks and benefits of ongoing pregnancy, and should be closely monitored by their healthcare provider.