What is the best approach for a patient's next Frozen Embryo Transfer (FET) cycle?

Approach to Subsequent Frozen Embryo Transfer Cycles

Continue with single embryo transfer (SET) in all subsequent FET cycles, regardless of the number of previous failed attempts, and do not modify your transfer strategy based on past outcomes. 1

Core Transfer Strategy

Number of Embryos to Transfer

• Transfer only one embryo per FET cycle, even after multiple failed attempts 1, 2
• The decision to transfer two embryos instead of one should never be based on:
  • Number of previous unsuccessful ART treatments 1
  • Duration of infertility 1
  • Previous pregnancies or live births from ART 1
  • Endometrial characteristics 1
  • Embryo quality in vitrified-warmed blastocyst transfers 1, 2

Blastocyst Transfer Protocol

• For vitrified-warmed blastocyst transfers, always perform SET regardless of blastocyst quality 1, 2
• This applies even to poor-quality blastocysts 1, 2
• Never transfer more than two embryos under any circumstances 1, 2

Endometrial Preparation Considerations

Cycle Type Selection

• Prioritize natural cycle FET (NC-FET) over artificial cycle FET (AC-FET) when the patient is ovulatory 3, 4
• NC-FET with corpus luteum present is associated with lower risk of preeclampsia and hypertensive disorders compared to AC-FET 3, 4
• AC-FET increases risks of preeclampsia and postpartum hemorrhage 4

Monitoring Requirements for Natural Cycles

• Measure luteinizing hormone (LH), estradiol, and progesterone to correctly time embryo transfer 5
• Urinary LH kits alone are unreliable and inadequate for optimal FET timing 5
• The LH surge varies widely in pattern, amplitude, and duration, and may not always result in corpus luteum formation 5

Artificial Cycle Protocol (When NC-FET Not Feasible)

• Continue estrogen until endometrial thickness reaches ≥7 mm 6, 7
• Begin progesterone supplementation only after achieving the ≥7 mm threshold 6, 7
• After positive pregnancy test, continue estrogen and progesterone at original doses for 3-4 weeks, then gradually taper to complete discontinuation within 2 weeks 6, 7

Pre-Transfer Evaluation

Uterine Cavity Assessment

• Perform saline infusion sonography (SIS) if more than 1-2 years have elapsed since last uterine evaluation 8
• SIS can detect endometrial polyps, uterine septum, intramural fibroids, and cervical stenosis 8
• Hysteroscopic correction of detected abnormalities improves clinical pregnancy rates (85.7% vs 54.1% in those with normal cavity) 8

Patient Counseling Requirements

Mandatory Discussion Points

• Counsel patients about medical, economic, social, and psychological consequences of multiple embryo transfer 1, 2
• Discuss risks of multiple pregnancy including:
  • Preeclampsia and gestational diabetes 1
  • Preterm labor and emergency cesarean section 1
  • Mental health complications postpartum 1
  • Increased direct and indirect healthcare costs 1
  • Neonatal intensive care admission and neonatal death 1

Informed Consent

• Obtain additional consent form if transferring more than one embryo 1
• Both partners should be involved in the decision-making process 1

Common Pitfalls to Avoid

• Do not increase embryo number after repeated failures - this is a strong recommendation against common practice 1
• Do not use double embryo transfer with planned fetal reduction - this strategy is not recommended 1, 2
• Do not base transfer decisions on ovarian response (low, normal, or high responders should all receive SET) 1
• Do not rely solely on urinary LH kits for NC-FET timing - serum hormone measurements are necessary 5