How to read fertility success rates

Start by asking: success per what?

A percentage may describe pregnancy or live birth; per embryo transfer, egg collection, started cycle or patient; using own eggs or donor eggs; and within a particular age group or time period. Two numbers that use different definitions should not be compared.

Age and case mix matter

Age at egg collection strongly affects population-level outcomes with a patient’s own eggs. Clinics also see different groups: some manage more complex diagnoses, repeated unsuccessful treatment or older patients. A headline rate can therefore reflect who was treated as well as how care was delivered.

• Ask for live birth, not only positive tests
• Ask whether cancelled cycles are included
• Separate own-egg and donor-egg results
• Look for age-specific groups
• Ask how many cycles produced the figure

Small numbers can look dramatic

When a clinic performs few cycles, one or two outcomes can move a percentage substantially. Multi-year information may be more stable but can hide recent changes. Regulators such as the HFEA standardise reporting because uncontrolled comparisons can mislead.

Use data to improve the consultation

A clinic should explain which published data are relevant to you, what the main uncertainties are and what outcome it is quoting. The most useful question is not “What is your best number?” but “Based on my assessment, which factors are likely to matter and how will you review the plan if treatment does not progress as expected?”