Glossary · Outcome Metrics · v2026.3
What is Cumulative Live Birth Rate (CLBR)?
CLBR is the single most meaningful outcome metric in IVF. It answers the question patients actually care about: what is the probability that this retrieval cycle will result in a baby?
Definition
Cumulative Live Birth Rate (CLBR) is the probability of achieving at least one live birth from all embryo transfers derived from a single ovarian stimulation cycle, including both fresh and frozen embryo transfers from that cohort.
Unlike per-transfer or per-cycle statistics, CLBR captures the total reproductive potential of one egg retrieval. If a retrieval produces five embryos, CLBR accounts for the probability across all five potential transfers: not just the first one.
This distinction is critical because modern IVF increasingly uses freeze-all protocols, meaning the first transfer from a retrieval may occur weeks or months later. A per-transfer rate captures only one data point. CLBR captures the entire investment.
The Physics: Why CLBR Matters More Than Per-Transfer Rates
IVF is a probabilistic system. Each step: stimulation, retrieval, fertilization, culture, transfer, implantation, has its own probability of success. The per-transfer live birth rate measures only the final step: what happens when you put one embryo into one uterus.
But patients do not experience IVF as a single transfer. They experience it as a cycle: one stimulation, one retrieval, and then however many transfers that cohort of embryos allows. CLBR measures the outcome across that entire sequence.
Consider two patients:
Patient A (age 32)
Retrieval yields 12 eggs → 8 mature → 6 fertilized → 4 blastocysts → 3 euploid. Per-transfer LBR: ~55%. CLBR across 3 transfers: ~87%.
Patient B (age 41)
Retrieval yields 5 eggs → 3 mature → 2 fertilized → 1 blastocyst → 1 euploid. Per-transfer LBR: ~50%. CLBR from this single retrieval: ~50%. To increase CLBR, Patient B may need multiple retrievals to bank more embryos.
The per-transfer rate is nearly identical. The CLBR tells a completely different story. This is why egg count and embryo yield matter, they determine how many attempts you get from one retrieval, which directly determines cumulative probability.
Clinics that report only per-transfer rates are showing you one frame from a film. CLBR shows you the whole film.
Data Anchor: SART National Summary
The primary US statistical source for CLBR is the SART (Society for Assisted Reproductive Technology) National Summary, published annually with a two-year reporting lag. SART collects outcome data from over 450 US IVF clinics covering approximately 95% of all US cycles.
SART 2022 National Summary data provides population-level CLBR estimates stratified by:
- • Patient age, the single strongest predictor of CLBR
- • Cycle type, autologous (own eggs) vs donor eggs
- • Diagnosis, male factor, diminished ovarian reserve, tubal factor, etc.
- • Fresh vs frozen transfers, modern freeze-all strategies have shifted the data distribution
Approximate CLBR ranges from SART data (autologous cycles, all embryo transfers from one retrieval):
| Age Group | Approximate CLBR |
|---|---|
| Under 35 | 65-75% |
| 35-37 | 55-65% |
| 38-40 | 40-50% |
| 41-42 | 25-35% |
| 43+ | 10-20% |
Note: These are population-level approximations. Individual CLBR depends on ovarian reserve, stimulation response, lab quality, embryo yield, and uterine factors. SART data is reported at a national aggregate level and should not be applied as individual prediction without adjustment.
Calculate Your Projected CLBR
Population-level CLBR data provides orientation. Individual projection requires incorporating your specific variables: age, AMH, antral follicle count, diagnosis, and prior cycle history.
The Decision Snapshot tool models your projected cumulative probability using structured inputs and SART-referenced outcome distributions.
Open Decision Snapshot tool →What CLBR Does Not Tell You
- • Time to live birth. CLBR does not indicate how many months or transfers it will take. A 70% CLBR might require one transfer or four.
- • Emotional or financial cost. Each additional transfer carries psychological and monetary weight that statistics do not capture.
- • Individual variability. CLBR is a population statistic. Your individual probability depends on factors SART data cannot fully resolve, including lab quality, embryologist skill, and endometrial receptivity.
- • Multiple retrievals. CLBR from a single retrieval is not the same as CLBR across multiple retrievals. Banking embryos from multiple cycles increases cumulative probability but also increases cost, time, and physical burden.
Frequently Asked Questions
What is CLBR in IVF?
CLBR measures the probability of achieving at least one live birth from all embryo transfers derived from a single egg retrieval cycle, including fresh and all subsequent frozen transfers from that cohort.
Why is CLBR better than per-transfer success rates?
Per-transfer rates measure a single event and ignore all other embryos from the same retrieval. CLBR captures the total reproductive potential of one stimulation cycle, giving a far more realistic picture of your chances.
What is a good CLBR?
CLBR varies by age. Under 35: 65-75%. Age 35-37: 55-65%. Age 38-40: 40-50%. Age 41-42: 25-35%. Age 43+: 10-20%. Individual results depend on ovarian reserve, lab quality, and embryo yield.
Where does CLBR data come from?
The primary US source is SART National Summary data, published annually with a two-year lag. International sources include ESHRE and ICMART.
Related reference
This content defines CLBR for educational orientation. Statistical ranges are approximate and based on SART National Summary aggregate data. Individual outcomes depend on diagnosis, protocol, and clinic-specific variables. This does not constitute medical advice.