Objective: The objective was to describe the efficacy of medical abortion using mifepristone and misoprostol for gestations less than 6 weeks.

Study design: We searched PubMed and Cochrane databases for articles in any language that examined the success of mifepristone and misoprostol abortion at gestational ages <42 days. Data were independently abstracted by two authors and graded for evidence quality. A pooled analysis of efficacy and a summary odds ratio of abortion failure of <42 days' gestation compared with gestational week 42-49 days were performed for randomized trials as well as for prospective studies.

Results: Six randomized controlled trials and nine prospective observational studies met inclusion criteria. Included studies varied greatly in regimens of mifepristone and misoprostol used, and assessment of and timing of outcome of abortion. A pooled proportion of the randomized trials estimated a proportion of unsuccessful abortion of 0.02 (95% confidence interval 0.01-0.03). In the prospective studies, the proportions ranged between 0.02 and 0.17, with considerable heterogeneity in the pooled estimate. However, the two largest observational studies reflected the estimates of the randomized trials (range 0.02-0.03). The summary odds ratios indicated that the odds of unsuccessful abortion were not significantly different between gestational age groups (<42 days versus >42-49 days).

Discussion: These analyses support the use of medical abortion at gestational ages <42 days. Efficacy rates are high overall and appear to reflect those observed during the seventh week of pregnancy. Women who prefer to initiate treatment as soon as early pregnancy is diagnosed may do so without delay.

Implications: Women can expect success using medical abortion regimens as soon as pregnancy is diagnosed; further research of abortion outcomes disaggregated by gestational age and visualization of the gestational sac is warranted.