ABCD • Analytical Blastocyst–Cleavage Decision

All model inputs are entered together in the Model Parameters panel. Values for c, b, C, and B are entered as percentages.

1. Baseline-stage embryo number (n)
   Enter the number of embryos available at the time the decision is made:
   2PN stage → enter n_2PN
   Cleavage stage → enter n_cleavage
   This defines the embryo cohort to which both strategies are applied.
2. Laboratory performance metrics (c and b)
   c (%): Probability that a baseline embryo becomes a transferable cleavage-stage embryo
   b (%): Probability that a baseline embryo becomes a transferable blastocyst
   Use your center’s observed rates whenever possible, preferably age-stratified.
3. Per-transfer live birth rates (C and B)
   C (%): Live birth rate per cleavage-stage single-embryo transfer
   B (%): Live birth rate per blastocyst-stage single-embryo transfer
   Ideally, these values should reflect your center's outcomes in patients of a similar age group, averaged across both fresh and frozen–thawed embryo transfer cycles.
4. Transfer tolerance (w)
   The parameter w reflects how strongly the patient prioritizes maximizing CLBR versus minimizing the number of transfers.
   Higher w → greater willingness to undergo repeated transfers to maximize CLBR
   Lower w → stronger preference to limit the number of transfers, even at the expense of some reduction in CLBR
5. Optional: mark up to two parameters as Unknown
   If one or two parameters are uncertain, mark them as Unknown to scan plausible values and see where the recommended strategy changes.

When all parameters are specified, the model displays the recommended transfer strategy (cleavage-stage or blastocyst-stage).

When one parameter is marked as Unknown, ABCD scans the full range of that parameter and reports:

• The recommended strategy at each value within the range
• The threshold point where the recommendation changes from cleavage to blastocyst (or vice versa)
• This feature is useful for exploring questions such as:
  • What minimum transferrable blastocyst rate is needed to favor blastocyst transfer?
  • How does the recommendation change with different levels of transfer tolerance?

When two parameters are marked as Unknown, ABCD generates a two-dimensional plot showing:

• The decision regions across the combined ranges of both parameters
• The boundary curve where the preferred strategy switches

In the special case where transfer burden is negligible (very large w), the decision simplifies to a CLBR-only comparison, showing which strategy yields the higher cumulative live birth probability. ABCD also displays these CLBR-only results alongside the main recommendations for easy comparison.

The default values on the site illustrate the following scenario:

• Decision point: 2PN stage
• Baseline embryos: n_2PN = 6

Laboratory performance (entered as percentages):

• c = 80% → 80% of 2PN embryos are expected to become transferable cleavage-stage embryos
• b = 30% → 30% of 2PN embryos are expected to develop into transferable blastocysts

Age-matched per-transfer live birth rates:

• C = 15% for cleavage-stage transfers
• B = 26% for blastocyst-stage transfers (averaged across fresh and frozen–thawed cycles)

Transfer tolerance:

• w = 15, meaning the benefit of achieving one live birth is considered equivalent to the cumulative burden of 15 embryo transfer procedures

After entering these values, ABCD calculates and displays the preferred transfer strategy.

If the clinician is uncertain about patient's transfer tolerance, w can be marked as Unknown. The updated results then show that:

• For w ≥ 14, the recommended strategy is cleavage-stage transfer
• For w < 14, the recommendation shifts to blastocyst-stage transfer

If two parameters—for example, b and w—are marked as Unknown, the model generates a plot showing how the recommended strategy changes across different combinations of transfer tolerance and blastocyst development rate. This visualization helps identify the minimum transferable blastocyst rate required to favor blastocyst-stage transfer at various levels of patient transfer tolerance.