Meta-analysis of the embryo freezing transfer interval

Area of Science:

• Reproductive Medicine
• In Vitro Fertilization (IVF)
• Embryology

Background:

• The optimal timing for frozen embryo transfer (FET) after oocyte retrieval (OPU) in IVF cycles remains debated.
• Uncertainty exists regarding the necessary recovery time for endometrial receptivity following ovarian stimulation.

Purpose of the Study:

• To investigate the impact of the interval between OPU and FET on IVF outcomes.
• To determine if delaying FET improves pregnancy and live birth rates.

Main Methods:

• A systematic electronic literature search was conducted across MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials.
• Studies published between January 1, 2007, and February 1, 2020, were included.
• Data on the influence of the interval between OPU/embryo freezing and FET were analyzed.

Main Results:

• Immediate FET cycles showed a trend towards increased biochemical pregnancy rates (RR=1.08).
• Clinical pregnancy rates were slightly higher in immediate FET cycles, but not statistically significant (RR=1.07).
• Live birth rates and implantation rates were similar between immediate and delayed FET groups.

Conclusions:

• Systematically delaying FET does not confer significant benefits for IVF outcomes.
• Immediate FET is associated with a trend towards better clinical pregnancy rates.
• Immediate FET potentially reduces psychological distress for patients by avoiding prolonged waiting periods.