Cleavage stage versus blastocyst stage embryo transfer in assisted conception

Area of Science:

• Assisted Reproductive Technology (ART)
• Embryology
• In Vitro Fertilization (IVF)

Background:

• Advances in understanding embryo nutrient needs have led to extended in vitro culture from 2-3 days to 5-6 days (blastocyst culture).
• Blastocyst culture aims to improve uterine-embryonic synchrony and select viable embryos.
• Clinical benefits of blastocyst culture since 1998 remain debated.

Purpose of the Study:

• To compare live birth and pregnancy success rates between blastocyst stage embryo transfers (ETs) and cleavage stage ETs.
• To identify factors influencing success rates in different embryo transfer stages.

Main Methods:

• Systematic review and meta-analysis of randomized controlled trials (RCTs) comparing early cleavage (Day 2-3) versus blastocyst (Day 5-6) stage transfers.
• Searched multiple databases including Cochrane, MEDLINE, EMBASE, and Bio extracts up to May 2005.
• Primary outcomes: live birth, clinical pregnancy, and multiple-pregnancy rates. Secondary outcomes: miscarriage, implantation, and embryo freezing rates.

Main Results:

• No significant difference in live birth rates (34.3% vs. 35.4%) or clinical pregnancy rates (38.8% vs. 40.3%) between Day 2-3 and Day 5-6 transfers.
• No difference in multiple-pregnancy rates (OR 0.85, 95% CI 0.63 to 1.13).
• Significantly higher rates of failure to transfer embryos in Day 5-6 transfers (10.1% vs. 3.5%), and significantly lower rates of embryo freezing.

Conclusions:

• No evidence supports a difference in live birth or pregnancy outcomes based on embryo transfer day (Day 2-3 vs. Day 5-6).
• Blastocyst transfer is linked to increased failure to transfer embryos and decreased embryo freezing.
• Insufficient data on cumulative live birth rates from fresh and thawed cycles prevents definitive conclusions on the overall advantage or disadvantage.