Most people are familiar with the fact that most couples who reach the point in an ART cycle when embryos are transferred to the uterus, will not achieve a pregnancy. Even when presumably high quality, fertile eggs are used, such as in egg donation, over half of couples are still left disappointed each cycle. Since most couples are able to get eggs and have fertilization, then the question is where does the failure occur? The answer may be in the implantation phase.
After a fertilized egg is returned to the uterus, several things must happen:
- It must continue to divide and grow (it is now called an embryo).
- The embryo must break out of the zona pellucida (usually just called the zona) which is a hard protein shell that surrounds it.
- The embryo must then burrow into the lining of the uterus (called the endometrium) and continue to grow there.
It is the published opinion of some scientists that, pregnancy may fail to occur in some cases because of an inability of the embryo to break out or "hatch" from the zona. According to the theory, there are some women who are more prone for this to happen.
These include women who:
... are over 40 years old
... have failed to implant in several IVF cycles.
... have eggs with very thick zona when measured under the microscope
and
... who have abnormal hormone profiles indicative of lower quality eggs (elevated FSH levels)
Logically then, if we could assist those embryos in the hatching process, it might be possible to increase the chance that implantation and hence successful pregnancy might occur. And so assisted hatching (AZH) was invented.
There are many different methods of AZH. At Rotunda - The Center for Human Reproduction, we use the Saturn Laser from Resona Instruments Ltd, UK.
