In order for implantation to occur, the embryo has to escape the shell (zona pellucida) surrounding it. This process is known as embryo hatching and it occurs in normal circumstances within the uterus. Assisted embryo hatching is a technique whereby the embryologist can precisely and accurately make an opening in the zona pellucida using a laser. This hole assists the hatching process by weakening the shell of the embryo. Assisted hatching is indicated:
- when the zona pellucida is noted to be excessively thick (>17 microns) when measured on a day 3 embryo
- frozen embryo transfer
- with poor embryo quality
- in women with an elevated Day 3 FSH
- when the female partner age is 39 or older at the time of stimulation, or
- with previous IVF implantation failures.
Assisted embryo hatching is generally performed on thawed embryos or blastocysts from frozen embryo transfer (FET) cycles. There is recent evidence supporting the use of assisted hatching in improving success rates as cryopreservation can result in hardening of the zona pellucida. This applies to all FET cycles regardless of method of cryopreservation (eg. vitrification, slow-freeze) or stage of embryo development (oocyte, zygote, cleavage stage or blastocyst) when cryopreserved.
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