Embryo grade · 4CB

4CB embryo: what the grade means.

4CB flips the mixed-letter pattern: expanded blastocyst with a C inner cell mass and B trophectoderm. Because ICM is associated with the fetal cell mass in teaching diagrams, C scores here raise sharp questions. Still, morphology is lab-local and not a personal probability from a marketing site.

Planning aid for family building — not medical advice, not a personal success rate, and not a clinical opinion for your case.

Gardner breakdown

4CB = expansion 4 · ICM C · trophectoderm B. Decode each field below, then use the interactive tool with this grade preloaded.

Reading guide

How to read a 4CB.

  • Expansion 4: expanded blastocyst.
  • ICM C: fewer cells or looser ICM appearance on that lab’s scale.
  • TE B: moderate outer-layer score.
  • Put the grade beside the full embryo list, ages of development, and any PGT narrative from your clinic.
Day 5 / 6 / 7

Same letters, different calendars.

Ask whether ICM C reflected a single scoring moment and whether the embryo was cultured further. Some reports capture the best TE/ICM combination available that day; others freeze promptly once expansion criteria are met.

Methodology

Gardner-style blastocyst grades describe how an embryo looks under the microscope on the day of freeze or transfer: expansion of the fluid cavity (1–6), quality of the inner cell mass that may become the fetus (A–C), and quality of the trophectoderm that becomes placenta (A–C). Morphology is one planning signal among many. It is not a personal success rate. Clinics differ in how they assign letters, and day-5, day-6, and day-7 embryos can carry the same letter string with different context. Society for Assisted Reproductive Technology (SART) clinic reports and peer-reviewed embryology literature discuss morphology alongside age, embryo cohort, and PGT when used — never grade alone as a prediction for your case.

Interactive decoder

Run 4CB in the decoder.

Manual entry · plain English

Paste a Gardner-style grade from your lab report (for example 4AA or D5 4AB). This translates fields into readable language — it does not score success odds.

Override individual Gardner fields
Decoded summary

Report grade entered as 4CB. In Gardner-style notation, 4CB describes expansion 4, ICM C, and trophectoderm B. This is a translation aid, not a ranking of embryo quality or a prediction of live birth.

Gardner-style blastocyst notation decoder with plain-English field translation. Educational only; clinic reports and counseling govern care.

Field-by-field

  • Day of development: Day 5
    Common blastocyst assessment day in many labs.
  • Expansion grade: 4
    Expanded blastocyst — larger cavity; zona thins as the embryo grows.
  • Inner cell mass (ICM): C
    Inner cell mass graded C — few cells; appearance is thinner or looser.
  • Trophectoderm (TE): B
    Trophectoderm graded B — moderate cell number / cohesion.
  • Stage: blastocyst
    Blastocyst-stage embryo (usual modern freeze / transfer stage).
  • PGT / genetic testing: untested
    No PGT result entered — morphology only.

What this tool will not do

  • No personal success percentage is computed from grade alone.
  • No red/green “good embryo / bad embryo” diagnosis.
  • No fertility score or ranking across patients.

Limitations

  • Lab grading systems and letter cutoffs are not fully standardized across clinics.
  • Morphology does not equal genetic status; PGT is a separate test on a biopsy sample.
  • A single grade does not predict your personal chance of pregnancy or live birth.
  • Clinic embryologists and REIs interpret grades in the context of your full cohort and protocol.

Questions for clinic / embryology

  • Can you walk me through how your lab defines this grade and how it ranks among my other embryos?
  • Was this embryo biopsied, and if so, what PGT platform and reporting categories do you use?
  • How do day-6 or day-7 blastocysts perform in your program compared with day-5?
  • What transfer order would you recommend given the full embryo cohort, not only this grade?
  • Are there lab photos or morphokinetic notes that change how I should read this line on the report?
  • How does this embryo rank within my full cohort for transfer order?

Planning aid for family building — not medical, legal, or tax advice, and not a clinical opinion for your case.

Clinic questions

Ask your team about this 4CB.

  • How does your lab counsel on ICM C blastocysts for transfer?
  • Would you prioritize a different sibling despite a lower expansion digit?
  • Is there video or photo documentation I can review with the embryologist?
Common questions

4CB FAQ.

Is ICM more important than TE?

Both matter and are interpreted together. Clinics disagree on exact weighting; your program’s policy is what applies to your case.

Should I discard a 4CB without asking?

No. Disposition decisions need clinical counseling. Public grade pages exist to help you ask better questions, not to authorize discarding embryos.

Does 4CB mean chromosomal problems?

Morphology is not a chromosome test. Only PGT or other genetic assays speak to chromosomal results, with their own limits and error modes.

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