What is the recommended approach for embryo BC (Blastocyst) grading in IVF (In Vitro Fertilization)?

Recommended Approach for Embryo Blastocyst Grading in IVF

Blastocyst trophectoderm biopsy with five to eight cells is the recommended standard for embryo grading in IVF, as it minimizes impact on embryonic development while providing sufficient material for genetic testing. 1

Optimal Biopsy Technique

• Blastocyst trophoblast cell biopsy is the main recommended method for embryo assessment in IVF cycles, as it has minimal effect on embryo development potential 1
• Biopsy should be performed on Day 5 or 6 after ICSI when the blastocyst is fully expanded 1
• The biopsy should be performed away from the inner cell mass to avoid damage to this critical structure 1
• Five to eight trophectoderm cells should be biopsied - this number balances the need for sufficient genetic material while minimizing impact on embryonic development 1

Blastocyst Grading System

• Blastocysts should be graded based on three key parameters: expansion stage, inner cell mass (ICM) quality, and trophectoderm (TE) quality 2, 3
• A simplified but clinically useful grading system categorizes blastocysts as:
  • Excellent: fully expanded with clear inner cell mass and cohesive trophectoderm
  • Good: not yet fully expanded but with clear inner cell mass and cohesive trophectoderm
  • Average/Poor: small inner cell mass and/or irregular trophectoderm 2

Predictive Value of Grading Components

• Inner cell mass (ICM) grade is the strongest predictor of live birth outcomes in single embryo transfers 4
  • Grade A ICM shows significantly higher live birth rates (54.6%) compared to grade B (41.3%) and grade C (28.5%) 4
• Trophectoderm (TE) grade is also important but secondary to ICM grade:
  • Grade A/B TE shows comparable outcomes (no significant difference between A and B)
  • Grade C TE shows significantly lower live birth rates compared to grades A and B 4
• Blastocyst expansion stage has some impact on outcomes:
  • Stages 4-5 (fully expanded) show better outcomes than stage 3 (early blastocyst) 4

Embryo Selection Algorithm

• For euploid embryos, prioritize selection based on overall blastocyst quality in this order:
  1. Excellent quality (≥3AA): highest ongoing pregnancy rate (84.2%)
  2. Good quality (3-6AB, 3-6BA, 1-2AA): good ongoing pregnancy rate (61.8%)
  3. Average quality (3-6BB, 3-6AC, 3-6CA, 1-2AB, 1-2BA): moderate ongoing pregnancy rate (55.8%)
  4. Poor quality (1-6BC, 1-6CB, 1-6CC, 1-2BB): lowest ongoing pregnancy rate (35.8%) 3

Clinical Considerations

• Even low-grade blastocysts can result in live births (30.2% live birth rate), though at lower rates than good-grade blastocysts (44.4%) 5
• Very low-grade blastocysts (CC grade) have significantly reduced live birth rates (13.7%) 5
• Importantly, low-grade blastocysts that achieve pregnancy do not show increased risk of adverse perinatal outcomes compared to good-grade blastocysts 5
• Single embryo transfer is recommended for patients with PGT-M to reduce multiple pregnancy risks 1

Quality Control Considerations

• Embryo grading should be performed by trained embryologists with regular quality control assessments 1
• Inter-observer agreement for simplified grading systems is substantial (K = 0.63) for grade allocation and clinical decision-making (K = 0.66) 2
• Intra-observer agreement ranges from substantial to almost perfect for grade allocation and clinical fate determination 2

By following these evidence-based recommendations for blastocyst grading, clinicians can optimize embryo selection for transfer, improving pregnancy outcomes while minimizing risks in IVF procedures.