When a fertility clinic says its success rate is 65%, what does that actually mean? The answer depends entirely on how that number was calculated — and there are at least five different ways to calculate it, each producing a meaningfully different result.

Understanding which metric you're looking at — and which one you should be looking at — is the single most important skill you can develop when researching IVF clinics.

The five ways clinics report success rates

The CDC collects data on IVF outcomes and allows clinics to report in several ways. Here's what each one means:

1. Per intended retrieval (the most honest metric)

This counts all patients who started an IVF cycle with the intent to retrieve eggs — including those whose cycles were cancelled before retrieval due to poor response, illness, or other reasons. Because it includes cancelled cycles in the denominator, this produces the most conservative and realistic success rate.

This is the metric FertilityMetrics uses and the one we recommend focusing on. A clinic reporting 45% per intended retrieval is telling you that 45 out of every 100 patients who walked in the door and started a cycle ultimately had a live birth.

2. Per egg retrieval

This excludes patients whose cycles were cancelled before eggs were retrieved. Because it removes the patients who responded poorly, the denominator is smaller and the rate looks higher. A clinic with a 15% cancellation rate might report rates 5–10 points higher using this metric versus per intended retrieval.

3. Per embryo transfer

This only counts cycles where eggs were retrieved AND embryos were successfully transferred. It excludes patients whose eggs didn't fertilize, didn't develop into viable embryos, or who didn't have embryos suitable for transfer. This produces the highest-looking numbers and is the most flattering to clinics.

4. Per cycle started

Similar to per intended retrieval but sometimes defined differently depending on what counts as "starting" a cycle. Ask clinics to clarify exactly what they mean by this.

5. Cumulative rate

This counts the percentage of patients who had a live birth after multiple cycles — typically two or three. Cumulative rates are significantly higher than single-cycle rates and are legitimate to consider, but should always be clearly labeled as such.

The age problem

Age is the single strongest predictor of IVF success. A clinic serving mostly patients under 35 will report dramatically higher rates than one serving older patients — not because it's a better clinic, but because its patient population is younger.

This is why comparing raw success rates between clinics without controlling for age is essentially meaningless. A clinic reporting 60% overall might serve 80% patients under 35. A clinic reporting 40% overall might serve a population skewed toward 38–42 year olds with diminished ovarian reserve.

Always compare rates within the same age group. The CDC reports data in four brackets: under 35, 35–37, 38–40, and over 40. FertilityMetrics shows rates by age group for every clinic so you can compare apples to apples.

The volume problem

A clinic reporting a 70% success rate from 12 patients is not the same as a clinic reporting 55% from 400 patients. Small samples produce unreliable statistics — a few lucky outcomes can swing the rate dramatically in either direction.

As a rough guide: fewer than 50 cycles in your age group means the rate should be treated as directionally interesting but statistically fragile. Over 100 cycles in your age group provides reasonable reliability. Over 200 gives you high confidence the rate reflects real patterns rather than random variation.

What "new patients" means

The CDC distinguishes between "new patients using their own eggs" and "all patients." New patient rates typically exclude frozen embryo transfers from prior cycles and patients who've already had multiple cycles at the clinic. This can make rates look better or worse depending on how the clinic's patient mix breaks down.

FertilityMetrics uses the "all patients, per intended retrieval" metric as its primary display — the most inclusive and conservative measure available in the CDC dataset.

The one question that cuts through everything

When speaking with a clinic, ask this: "What is your live birth rate per intended egg retrieval for patients in my specific age group, and how many patients did you treat in that group in the most recent year?"

The rate and the volume together tell you what you actually need to know. A high rate with low volume deserves skepticism. A moderate rate with high volume is often more reliable than a high rate from a small sample.

What success rates can't tell you

Success rates reflect what happened to past patients, not what will happen to you. They don't account for your specific diagnosis, your egg quality, your partner's sperm parameters, your uterine anatomy, or any of the clinical factors your physician will evaluate.

They're a starting point for research and a tool for comparison — not a prediction. Use them to narrow your list and ask better questions, then let your physician guide the clinical decision.