A decision framework for personalizing cleavage- or blastocyst-stage single-embryo transfer (SET) by integrating cumulative live birth probability with the expected burden of repeated transfers.
Sequential elective SETFirst-transfer LBR inputsSequential-transfer assumptions2PN or cleavage baseline
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Decision-support only. The tool expresses the assumptions in the accompanying decision model. It does not replace individualized clinical counselling, centre-specific validation, embryo assessment, or shared decision-making.
What this model compares
Two strategies, one starting cohort. The model compares cleavage-stage and blastocyst-stage single-embryo transfer (SET) policies beginning with the same cohort of n embryos at the selected decision point (2PN or cleavage stage).
Under the cleavage-stage strategy, embryos that become transferable at cleavage stage are used sequentially for SET. Under the blastocyst-stage strategy, embryos are cultured to blastocyst stage and transferable blastocysts are used sequentially for SET. Each route continues until a live birth occurs or no transferable embryos remain.
The comparison combines the cohort-level chance of at least one live birth with the expected number of transfer procedures. It is a transparent decision-analysis aid based on the entered scenario; it is not an individualized prognosis or a substitute for clinical counselling.
Model inputs
Start with point estimates (%) for a deterministic scenario, or choose observed events / totals to calculate input and model-output confidence intervals. C1 and B1 are first-transfer LBRs; the primary model assumes lower LBRs at later transfer orders.
Primary model
Abbreviations: 2PN, normally fertilized two-pronuclear zygote; SART, Society for Assisted Reproductive Technology; DOR, diminished ovarian reserve; LBR, live birth rate; SET, single-embryo transfer; CLBR, cumulative live-birth rate.
Decision point and SART-DOR age preset
At the 2PN decision point, the transferable cleavage-stage and blastocyst rates (c2PN and b2PN) are calculated per normally fertilized 2PN zygote: the number of zygotes is the denominator, and the number that reaches each transferable stage is the numerator.
SART 2014–2024, DOR-restricted first-IVF/first elective SET event counts and rates used in the manuscript. The >42-year preset is intentionally omitted.
Embryo availability and transfer preference
embryos
Number of embryos available at the selected decision point.
transfer-equivalents
Relative value of one live birth versus the cumulative burden of one transfer.
Laboratory conversion and transfer-specific LBRs
Select “Use observed events / total” on each input supported by numerator–denominator data. Unselected parameters remain fixed percentages. For the SART threshold analyses, select C1 and B1 as observed; keep c fixed at 80% for a 2PN baseline or 100% for a cleavage-stage baseline. b remains the numerically solved threshold.
%
95% Wilson CI: —
Probability that one 2PN embryo becomes a transferable cleavage-stage embryo. This composite rate may incorporate development, transfer eligibility, and, when relevant, post-warming survival.
%
95% Wilson CI: —
Probability that one 2PN embryo becomes a transferable blastocyst-stage embryo. This composite rate may incorporate development, transfer eligibility, and, when relevant, post-warming survival.
%
95% Wilson CI: —
Live birth probability at the first cleavage-stage transfer.
%
95% Wilson CI: —
Live birth probability at the first blastocyst-stage transfer.
How to define c and b at the selected baseline
At a 2PN decision point: c2PN is the probability that one normally fertilized two-pronuclear zygote yields a transferable cleavage-stage embryo; b2PN is the probability that it yields a transferable blastocyst-stage embryo. Both are composite, strategy-specific yields and can incorporate development, transfer eligibility, and, when relevant, post-warming survival.
At a cleavage-stage decision point: ccleavage is the probability that one baseline cleavage-stage embryo is available as a transferable cleavage-stage embryo, whereas bcleavage is the probability that it ultimately yields a transferable blastocyst-stage embryo. The default ccleavage=100% is appropriate only when every selected baseline cleavage-stage embryo is already transfer-eligible; enter a lower value when additional eligibility, cryosurvival, or other losses remain possible before SET.
Confidence-interval settings
draws
%
Input-rate intervals use the Wilson method. Modeled outcome intervals are percentile-based 95% parametric-bootstrap confidence intervals: only inputs selected as observed event / total are resampled, while all remaining parameters are held fixed. For threshold intervals, b is always the numerically solved target and is not resampled. Threshold searches use b∈[0,1]; draw-specific thresholds of 0 and out-of-range thresholds above 100% are retained in percentile calculations.
Alternative model: constant-probability approximation
Choose this approximation only when first-transfer or transfer-order-specific LBR information is unavailable but an average LBR per cleavage-stage SET and an average LBR per blastocyst-stage SET are available. In this mode, C and B are entered as those average LBRs and are used unchanged at every transfer order; rC and rB are not used.
Assumption: success is lower at later transfer orders. C1 and B1 are the live-birth probabilities at the first SET. In the primary model, after each unsuccessful SET, the odds of live birth at the next transfer are multiplied by rC or rB: oddsS,j = oddsS,1 × rSj−1. Therefore, rS<1 yields a lower LBR at the second, third, and later transfers. The LBR percentage itself is not simply multiplied by rS; the odds are.
This is a scenario assumption about the observed sequence of transfers, not a causal claim that one failed transfer lowers the biological chance of the next embryo. In practice, embryos with higher apparent developmental potential, more favourable morphology, or greater clinical priority are often transferred earlier. Patients who reach later transfers may therefore receive lower-priority embryos or differ in residual, unmeasured patient/cohort characteristics. The default values rC=0.85 and rB=0.80 were informed by transfer-order patterns reported by Dhaenens et al. Dhaenens L, et al. Hum Reprod. 2025;40(5):818–833.
Ready.
Results
ABCD strategy comparison
Calculated outputs are shown after the input panel so the sequence remains: choose the scenario, then review the pathway and model results.
Composite recommendation
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Enter a scenario and calculate results.
Embryo-development pathway
The selected baseline cohort is evaluated through the cleavage-stage SET route and the blastocyst-stage SET route for the current scenario.
Current scenario
ⓘThe cleavage and blastocyst conversion rates are expressed per selected baseline embryo.
Strategy-specific outcomes
C1 and B1 are first-transfer LBRs. CLBRC(n) and CLBRB(n) denote the strategy-specific cumulative live-birth probabilities (CLBRs) from the same cohort of n baseline embryos; they are shown below. The first row is a single-baseline-embryo probability, not CLBR.
Cleavage-stage SET route
C↑
One baseline embryo → first-transfer live birth probability under the cleavage strategy (c × C1)—
Cumulative live-birth probability (CLBR), CLBRC(n)—
Expected transferable embryos, E(KC) = n × c—
Expected transfers, E(TC)—
ABCD score—
For one baseline embryo, this requires cleavage-stage transferability and a live birth at its first possible SET; later embryos and later transfer orders are not included.
ABCDC(n) = w × CLBRC(n) − E(TC)
Blastocyst-stage SET route
B↑
One baseline embryo → first-transfer live birth probability under the blastocyst strategy (b × B1)—
Cumulative live-birth probability (CLBR), CLBRB(n)—
Expected transferable embryos, E(KB) = n × b—
Expected transfers, E(TB)—
ABCD score—
For one baseline embryo, this requires blastocyst-stage transferability and a live birth at its first possible SET; later embryos and later transfer orders are not included.
ABCDB(n) = w × CLBRB(n) − E(TB)
Blastocyst minus cleavage
Δ CLBR
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Δ expected transferable embryos
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Δ expected transfers
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Δ ABCD score
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Visual comparison of cumulative benefit, transfer burden, and ABCD score
Compare the two strategies directly. Higher cumulative live-birth probability (CLBR) and higher ABCD score are favourable; fewer expected transfers are favourable.
w = — transfer-equivalents per live birth
Cleavage-stage strategyBlastocyst-stage strategyBar lengths share a scale within each row; exact values are shown at right.
The ABCD score weights the cohort-level chance of at least one live birth by w and subtracts the expected number of transfer procedures.
How cumulative live-birth probability and transfer burden are calculated
For each possible number of transferable embryos, the primary model calculates the probability of achieving at least one live birth using the live-birth probability appropriate to each sequential transfer order. Those results are then averaged across the binomial distribution of the number of transferable embryos.
Expected transfers count every SET that would occur before the first live birth or exhaustion of the embryo cohort, including zero when no embryo becomes transferable. The optional constant-probability approximation instead applies the same average LBR at every transfer order.
Minimum transferable blastocyst-rate thresholds
Thresholds are solved numerically for the current scenario.
CLBR-only threshold
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ABCD-score threshold
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Confidence intervals from observed inputs
Observed input n/N, percentages, and Wilson intervals are shown in the pathway. Inputs left as percentages remain fixed; model-output intervals are shown next to their corresponding results.
95% CI
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Method note. Input-rate intervals use the Wilson method. Model-output intervals are percentile parametric-bootstrap 95% CIs; only inputs selected as observed are resampled, while all other scenario parameters remain fixed.
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Stage-specific live-birth probabilities by sequential transfer order
Live-birth probabilities for cleavage-stage and blastocyst-stage SETs at each possible position in the current sequential transfer sequence.
Transfer order
Cleavage, Cj
Blastocyst, Bj
Uncertainty exploration
Select one or two inputs above to visualize how the recommended strategy changes. Ranges are not confidence intervals.