The Association for Fertility and Reproductive Health of Nigeria had its annual conference last week. They covered several topics from guidelines and regulation of the practice of assisted reproductive technologies to new techniques in the field.
I will cover some of them in the next series of publications. The first one I want to touch now is the use of ART to test for abnormalities in human chromosomes by testing the embryos.
Medical Art Centre, in an earlier publication, discussed the effectiveness of PGT as a technology used in the selection of embryos with genetic defects and chromosomal abnormalities.
This technique was first introduced at the centre in 2009 and has yielded healthy babies that are sickle cell anaemia free and/or have accurate chromosome number. Recently, a new technique which yields better result with the PGT process was introduced by the centre. The following example would be considered for a better understanding of the new technique.
What is PGT?
PGT is an acronym for pre-implantation genetic testing. This involves techniques used to test embryos for genetic defects or chromosomal abnormalities prior to transferring them to the uterus. These embryos are usually created via In-Vitro Fertilisation. PGD and PGS are examples of PGT.
PGD versus PGS
Pre-implantation genetic diagnosis specifically refers to testing for specific gene defects in the DNA code. For example, PGD can be done on embryos from a couple where both partners are known carriers of a specific genetic disorder such as sickle cell anaemia, cystic fibrosis etc. On the other hand, Pre-Implantation Genetic Screening refers to testing that investigates the chromosome number abnormalities (aneuploidy testing) or the sex of the embryo.
In order for this diagnosis to be carried out, cell(s) must be taken out of the embryo. The process of taking out these cells is called biopsy. Before now, biopsy was usually performed on cleavage-stage embryos on the third day.
Embryo biopsy is traumatic and lowers the embryo’s ability to implant. With the advent of trophectoderm biopsy technique, cell removal can be performed on a blastocyst – stage embryo on the fifth or sixth day after fertilisation.
Trophectoderm biopsy involves the removal of the trophectoderm component (cells that form the placenta) of the blastocyst embryo. This is less traumatic and the blastocyst cells which are quite resilient recover quickly. Since the embryo has many more cells at the blastocyst stage (about 100 cells) than at the cleavage stage (6-10), we can remove about four-five cells from a blastocyst with little or no impact on its developmental potential.
How is trophectoderm biopsy done?
The story of a couple below will be used to illustrate the process.
“Eric and I have been together for several years without a baby. We were introduced to Medical Art Center by a close friend and we immediately started screening and management for infertility. After undergoing the IVF process, I got pregnant and delivered a baby girl three years ago. In order to balance our family, we opted for another round of IVF but this time around with the PGS option.
“We were particular about screening our embryos for chromosomal abnormalities since I am advanced in age and we also desired to have a male child. During the counselling process, we were advised to screen our embryos using array comparative genomic hybridisation (aCGH) which screens all 24 chromosomes.
“The consulting doctor explained to us that the clinic had just introduced a new biopsy technique which would increase our chances of having results for all our embryos. This technique will reduce the incidence of embryo testing showing no signals or no results after diagnosis because usually four- five cells are available for testing after trophectoderm biopsy.
“We were told that we would be the first couple to use this technique for PGS at the clinic. The doctor went ahead to inform us that our embryos would be frozen via a technique called vitrification and would be transferred in a new cycle. That meant that we would not be having a fresh embryo transfer but, instead, a frozen-thawed embryo transfer. The doctor also assured us of the effectiveness of the vitrification process, hence calming our fears of fresh embryos being more viable than the frozen embryos.
We trusted the advice of the doctor and signed the written consents for the procedure. We underwent the IVF process, our embryos were cultured for five days and then biopsy was performed.
First, the embryo had to show a distinct inner cell mass (ICM) and trophectoderm. ICM forms the embryo proper and must be avoided during the biopsy process. A very small hole was made in the outer shell of the embryo using a laser. Then the trophectoderm cells were allowed to come out of the expanded blastocyst. Using a pipette and more laser beams, herniating trophectoderm cells were detached and used for diagnosis. At the blastocyst stage, the embryo is ready to implant and cannot be left to continue growing in the incubator, hence the need for embryo freezing. Our biopsied embryos were immediately frozen.
“At every stage of the process, we were updated on the progress of our embryos, from number of eggs retrieved to number fertilised then the number of embryos biopsied and frozen. Once the results were ready, we were called in for a consult. We were given a copy of the PGS report and the genetic counsellor explained our report. We were told explicitly the number of embryos that were chromosomally normal (euploid) and asked to decide what we wanted at transfer.
Two top quality euploid embryos were transferred in a subsequent cycle, pregnancy was confirmed two weeks later and we had our healthy baby boy in August 2015.”