Glossary · Definition · v2026.3
Cycle Start in IVF Reporting
Cycle start is the point at which an IVF cycle officially begins, typically defined as the first day of stimulation medication. It is the broadest denominator for success rate reporting.
Why Cycle Start Matters
Success rates reported per cycle start include all patients who began stimulation, including those who cancelled before retrieval or had no eggs fertilize. This makes per-cycle-start rates the most conservative and comprehensive reporting method. They reflect the true probability of success from the point of committing to a cycle.
Biological Constraints
Not all started cycles reach retrieval. Cancellation may occur due to poor response, excessive response, or elevated progesterone. Per-cycle-start rates are lower than per-retrieval or per-transfer rates because they include these cancelled cycles in the denominator.
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This content defines terminology for educational orientation. It does not constitute medical advice.
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