All methods of medication abortion have an associated failure rate.
A medication abortion is considered to have failed if an aspiration intervention
is required. Reasons for aspiration intervention include prolonged
or excessive bleeding, incomplete abortion (remnants of fetal tissue
in the uterus), or an ongoing pregnancy.
For the mifepristone/misoprostol and methotrexate/misoprostol regimens,
ongoing pregnancy occurs in less than 1% of cases. However, aspiration
intervention (and therefore medication abortion failure) is required
for 2%-5% of users of mifepristone/misoprostol, approximately 5% of
users of methotrexate/misoprostol, and approximately 10%-35% of misoprostol-only
users. The rates of aspiration intervention (for all medication abortion
methods) increase with increased gestational age.
