The ability of the embryo to 'hatch' from its protective shell is a crucial step in enabling it to implant in the uterus. We are fortunate to have an established technology that allows us to help the hatching process when necessary.
The egg's shell has a number of functions, the last of which is to hatch or 'free' the growing embryo so that it may implant. Initially, the egg's shell or zona pellucida is responsible for creating a barrier so that no more than one sperm fertilizes the egg (penetration by multiple sperm will almost inevitably destroy an embryo). The shell also functions to protect and encase the embryo as it grows from a mere 2 cells into approximately 8 cells 2-3 days after retrieval. When the embryo reaches the blastocyst stage (100-200 cells) approximately 5 days after retrieval, it is transferred to the woman's uterus. Here, the shell must be able to hatch the embryo so that it may adhere to the uterine wall, implant itself into the uterine lining and continue to grow.
When is Assisted Hatching used?
Any number of factors may prevent an embryo from developing and hatching successfully. Assisted hatching has been shown to be most helpful prior to transferring a frozen-thawed embryo, because the zona pellucida hardens with freezing. The zona is often harder in women that are older so we will often perform assisted hatching on embryos of women 38 years of age and older, especially with Day 2 or Day 3 embryo transfers. We will also hatch Day 2 or 3 embryos of younger women if the zona is thick or if the embryo quality is less than stellar. It is more difficult and possibly harmful to try to hatch fresh blastocyst-stage embryos. If older women are having a blastocyst-stage embryo transfer, we will only hatch if the zona pellucida is especially thick.
How is assisted hatching performed?
Assisted hatching is performed in the laboratory just before embryos are transferred into the woman's uterus. Using a laser, the embryologist makes a tiny, precise opening in the shell of each embryo.
Is assisted hatching safe?
Because the shell is not a living part of the embryo, penetrating this outer structure poses virtually no threat. Studies indicate that assisted hatching using laser technology is superior to chemical assisted hatching, in which the egg is penetrated with an acidic solution. Laser technology enables far more precision and is also done more quickly, thus reducing the length of time that embryos are handled before transfer. The laser also enables embryologists to prevent excessive heat exposure, thus eliminating virtually all risk to the embryo.
- J Assist Reprod Genet. 2011 February; 28(2): 119–128. Assisted hatching in assisted reproduction: a state of the art. Mohamad Eid Hammadeh,1 Constanze Fischer-Hammadeh,1 and Khaled Refaat Ali2
- Cochrane Database Syst Rev. 2009 Apr 15;(2):CD001894. Assisted hatching on assisted conception (IVF and ICSI). Das S, Blake D, Farquhar C, Seif MM. St Mary's Hospital, Hathersage Road, Manchester, UK