Understanding IVF success rates

What Is a Success Rate?

When the CDC reports a clinic's "success rate," it means the percentage of ART cycles that resulted in a live birth. The formula is:

Success Rate = (Live Births ÷ Cycles Started) × 100

So if a clinic started 100 IVF cycles and 42 resulted in at least one live-born baby, their success rate is 42%.

This is different from:

• Pregnancy rate - higher than live birth rate because some pregnancies end in miscarriage
• Implantation rate - even higher, as not all implantations result in a continuing pregnancy
• Fertilization rate - measures whether eggs fertilized, not whether a baby was born

The CDC's live birth rate is the most clinically meaningful number for patients asking "what are my chances of bringing a baby home?"

Why Age Group Is Everything

Age is the single strongest predictor of IVF success. The chart above uses the same CDC age bands PlainFertility shows on every clinic page:

• Under 35 - Highest clinic-mean live-birth rates in this extract (about 48%)
• 35–37 - Still relatively strong (about 35.3%)
• 38–40 - Declining (about 22.5%)
• Over 40 - Much lower with own eggs (about 8.8%)

The reason is egg quality. As people age, eggs are more likely to carry chromosomal abnormalities. Chromosomally abnormal embryos either fail to implant or result in early miscarriage. No clinic or technology fully overcomes this biological reality.

Critical rule: Only compare clinics within the same age group. A clinic with a 38% rate for under-35 patients and one with 42% for the same group are genuinely different. But comparing a clinic's under-35 rate to another clinic's overall rate is meaningless.

What the CDC Publishes, and What It Doesn't

The CDC's National ART Surveillance System (NASS) collects data from every fertility clinic in the US under the Fertility Clinic Success Rate and Certification Act of 1992. Reporting is mandatory.

The CDC reports:

• Live birth rates by age group
• Fresh vs. frozen cycle counts
• Whether donor eggs were used
• Single embryo transfer percentages
• Total cycle volume

The CDC does not report:

• Patient diagnoses or case complexity
• Specific laboratory techniques
• Cost per cycle
• Patient satisfaction

This matters because a clinic treating more complex cases, older patients, recurrent implantation failure, severe male factor infertility, will appear to have lower rates even if they are providing excellent care.

Fresh vs. Frozen Cycles

IVF involves two potential transfers: a fresh transfer in the same cycle as egg retrieval, or a frozen-thaw transfer (FET) using embryos cryopreserved for later use.

Modern vitrification (ultra-rapid freezing) has made frozen embryo transfers highly effective. Many clinics now prefer a "freeze-all" strategy, freezing all embryos and doing a FET in a later cycle when the uterine environment may be more receptive. FET success rates often match or exceed fresh transfer rates at experienced centers.

When comparing clinics, check both fresh and frozen rates if available. A clinic with primarily frozen transfers may have different numbers than one using primarily fresh transfers.

Volume Matters Too

A clinic's cycle volume tells you how much experience their team has. A clinic doing 20 cycles per year and one doing 500 cycles per year are operating at very different experience levels, even if their reported success rates appear similar.

High-volume centers often have more experienced laboratory staff, more opportunities to refine protocols, and more data to inform clinical decisions. This does not automatically make them better, some specialized smaller practices are excellent, but volume is worth noting.

The Single Embryo Transfer Signal

Single embryo transfer (SET) rate is one of the most underappreciated quality signals in fertility medicine. Transferring multiple embryos increases the chance of pregnancy in any one cycle, but also dramatically increases the risk of twins or triplets, which carry serious health risks for both mother and babies.

Evidence-based practice is to transfer one embryo at a time, especially in patients with favorable prognosis. A clinic with a high SET rate and a competitive success rate is doing something right: achieving good outcomes without taking shortcuts that put patients at risk.

If a clinic has an unusually high success rate but a very low SET rate (meaning they routinely transfer multiple embryos), factor that in. Their rate is inflated by higher-order transfer risk.

Donor Egg vs. Own Egg

Cycles using donor eggs have substantially higher success rates, often 50–70% - because the eggs come from young, screened donors. The CDC reports donor egg cycles separately.

Some clinics have higher overall success rates partly because they perform more donor egg cycles. This is not a quality difference, it is a case mix difference. When comparing clinics, use the same-egg-type, same-age-group data.

Common Mistakes When Comparing Clinics

• Comparing different age groups. A 45% rate for under-35s is not better than a 38% rate for 38–40s. Compare your age group only.
• Ignoring volume. A clinic with 50 cycles reporting 60% success has very few data points. Small numbers produce highly variable rates.
• Mistaking marketing for data. CDC data is the only standardized, audited source. Clinic websites may show different metrics.
• Ignoring single embryo transfer rates. High success + high SET = genuinely good outcome. High success + low SET = inflated by multiple transfers.
• Using stale data. Technology changes quickly. Check the report year.

How to Use PlainFertility Data

PlainFertility presents CDC NASS data in a standardized, searchable format. For each clinic you can see:

• Success rates by age group (Under 35, 35–37, 38–40, Over 40)
• Total cycle volume
• Fresh and frozen cycle breakdown
• Single embryo transfer percentage
• Donor egg availability
• Historical trend (where available)

Use these data points as one input among many. They are best used to build a shortlist of clinics to consult, not to make a final decision.