Cumulative chances across several cycles
What you are told depends entirely on what is assumed about the people who stopped.
Cumulative success rates sound simple and are not, because the people who leave treatment have to be counted somehow, and they left for reasons.
A study of 6,164 patients through 14,248 cycles at one large centre reported two figures after six cycles, and named its assumptions:
| After six IVF cycles | Optimistic estimate | Conservative estimate |
|---|---|---|
| All patients | 72% (95% CI 70 to 74) | 51% (95% CI 49 to 52) |
| Under 35 | 86% | 65% |
| 40 and over | 42% | 23% |
The optimistic method assumes the patients who did not come back would have done as well as those who did. The conservative method assumes none of them would have had a live birth. The truth lies between them, and the width of that gap is the honest uncertainty.
The largest study ever done, 156,947 UK women through 257,398 cycles, used a third method that assumes 30% of those who stopped had no chance. Its prognosis-adjusted figures:
| Group | Live birth, first cycle | Cumulative by sixth cycle |
|---|---|---|
| All women | 29.5% | 65.3% |
| Under 40, own eggs | 32.3% | 68.4% |
| 40 to 42 | 12.3% | 31.5% |
There is no wrong answer to that question, but there is a wrong answer to not asking it. A cumulative figure with no stated assumption about dropouts is not a number you can use.