Deep-freezing and transfer of human embryos

Area of Science:

• Reproductive biology
• Cryobiology
• Embryology

Background:

• Cryopreservation of human embryos is crucial for assisted reproductive technologies.
• Optimizing survival rates of early-stage human embryos post-thaw is essential for successful pregnancies.

Purpose of the Study:

• To evaluate the efficacy of specific cryopreservation techniques for four-cell and eight-cell human embryos.
• To determine optimal cooling and warming rates for maximizing embryo survival and pregnancy rates.

Main Methods:

• Cryopreservation of 162 four-cell and eight-cell human embryos using controlled cooling to -80°C in 1.5 M dimethylsulfoxide (DMSO).
• Controlled thawing from -80°C to +4°C at specific rates.
• Morphological assessment of surviving embryos using light and electron microscopy.
• Embryo transfer of surviving embryos to assess pregnancy rates.

Main Results:

• Survival rates were highest when embryos were cooled at 0.3°C/min to -80°C and thawed at +8°C/min from -80°C to +4°C.
• Embryo cryoinjury correlated well with morphological appearance under a dissecting microscope.
• 50% of embryos (68 of 136) survived with at least half of their blastomeres intact.
• Transfer of 68 surviving embryos resulted in nine pregnancies (20% pregnancy rate).

Conclusions:

• Specific controlled cooling and warming rates in the presence of DMSO are effective for human embryo cryopreservation.
• Morphological assessment post-thaw can predict embryo viability.
• Cryopreservation of early-stage human embryos using these methods can lead to successful pregnancies.