What is the most accurate estimate of pregnancy rates in IVF dropouts?

BACKGROUND: Dropouts in IVF-programmes affect cumulative pregnancy rates (CPRs), but it is unknown what the impact of loss to follow-up is. METHODS: Data were obtained from 588 couples starting IVF treatment ('as treated group'). Cycle-based and real-time-based CPRs were calculated using three assumptions for dropouts: dropouts having no probability of pregnancy, dropouts having the same probability of pregnancy as those continuing treatment and dropouts stopping because of medical reasons having no chance of pregnancy and those stopping because of other reasons having the same probability of pregnancy as those continuing treatment. CPRs obtained in the 'as treated group' were compared with CPRs calculated using the data set including the follow-up data of the dropouts ('completed group'). RESULTS: In 1.7% of couples, no follow-up could be obtained. The cycle-based CPR after three IVF-cycles ranged from 63% to 71% in the 'as treated group' and was 65% in the 'completed group'. The real-time-based CPR after 9 months ranged from 54% to 59% in the 'as treated group' and was 55% in the 'completed group'. The PR in dropouts was 14% (95% confidence interval 8.22%). CONCLUSIONS: In IVF programmes, outcome data of dropouts remain unknown, and CPRs should be calculated by assuming dropouts to have a PR between no probability and the same probability as those who continue treatment. Our study shows that the most accurate estimate for the PR in dropouts is 14%.