For In Vitro Fertilization (IVF), is a frozen embryo transfer (FET) in a subsequent cycle more recommended than a fresh embryo transfer in the same cycle?

Frozen Embryo Transfer in a Subsequent Cycle is Recommended Over Fresh Embryo Transfer for IVF

For IVF procedures, a frozen embryo transfer (FET) in a subsequent cycle is generally preferred over fresh embryo transfer in the same cycle as egg retrieval, with single embryo transfer (SET) being the recommended approach regardless of embryo quality.

Frozen vs. Fresh Embryo Transfer

• Frozen embryo transfer may be associated with better clinical outcomes compared to fresh embryo transfer, with studies showing higher live birth rates (RR 1.18,95% CI 1.08-1.30) and clinical pregnancy rates (RR 1.10,95% CI 1.02-1.19) 1
• FET significantly reduces the risk of ovarian hyperstimulation syndrome (OHSS) compared to fresh embryo transfer (RR 0.22,95% CI 0.12-0.39) 1
• The Cochrane review indicates that there is probably little or no difference in cumulative live birth rates between "freeze all" strategy and conventional IVF/ICSI strategy with fresh transfer 2
• However, FET may be associated with increased risk of hypertensive disorders of pregnancy and having larger-for-gestational-age babies 2

Number of Embryos to Transfer

• Single embryo transfer (SET) should be applied in vitrified-warmed blastocyst transfer cycles regardless of the quality of the vitrified blastocyst 3
• The European Society of Human Reproduction and Embryology (ESHRE) guidelines strongly recommend against transferring more than two embryos in any IVF cycle 3
• In frozen embryo transfer cycles, the decision to perform double embryo transfer (DET) instead of SET should not be based on endometrial characteristics 3

Endometrial Preparation for Frozen Embryo Transfer

• Recent evidence suggests that natural, modified natural, and artificial cycle endometrial preparation strategies in ovulatory women undergoing FET result in similar livebirth rates 4
• The livebirth rate after one FET was 37% in natural cycle, 33% in modified natural cycle, and 34% in artificial cycle preparation strategies 4

Special Considerations

• For patients using donor oocytes or donated embryos, only elective single embryo transfer (eSET) should be practiced 3
• For gestational carriers, only eSET should be practiced, and both carriers and intended parents should be counseled that double embryo transfer is associated with greater risk of pregnancy and perinatal complications 3
• The decision to perform double embryo transfer instead of single embryo transfer should not be based on:
  • Number of previous unsuccessful ART treatments 3
  • Duration of infertility 3
  • Previous pregnancies or live births from ART 3

Common Pitfalls and Caveats

• By design, time to pregnancy is shorter in the conventional strategy with fresh embryo transfer than in the "freeze all" strategy when the cumulative live birth rate is comparable 2
• The transfer of two or more embryos with the intention of performing fetal reduction in case of multiple embryo implantation is not recommended 3
• Patients should be counseled about the medical, economic, social, and psychological consequences of transferring multiple embryos 3
• While frozen embryo transfer may reduce OHSS risk, it may increase the risk of hypertensive disorders of pregnancy and having larger babies 2

Algorithm for Decision Making

1. Assess patient-specific factors (age, ovarian response, previous IVF outcomes)
2. For most patients, plan for a "freeze all" approach with subsequent frozen embryo transfer
3. Use single embryo transfer for frozen blastocyst transfers regardless of embryo quality 3
4. Consider endometrial preparation method based on patient preference and clinic protocols, as outcomes appear similar between natural, modified natural, and artificial cycles 4
5. Mandatory single embryo transfer for donor oocyte cycles, donated embryo cycles, and gestational carrier arrangements 3