Pre-Implantation Genetic Screening Q&A
I have no fertility problem. Why is my chance of pregnancy not 100%?
We have found that even patients with normal fertility in the past make abnormal pre-embryos. When processing the cell or cells removed from the pre-embryo, these cells are tested for other common chromosomal problems that can result in an abnormal pregnancy. Of course, the genetically abnormal pre-embryos cannot be transferred into the mother.
Pregnancy rates in humans decrease with age. One reason for this is that the eggs available for conception were made prior to birth. The chromosomes in these immature eggs are in a state of arrested cell division that when prolonged more than 32 years starts to result in more genetically abnormal eggs. That is why we also see increased rates of miscarriage as well as increased rates of chromosomally abnormal babies as mothers get older. [Down’s syndrome results from an egg that matured containing two copies of chromosome # 21. When a normal sperm fertilizes this egg and adds another chromosome #21, the resulting embryo, fetus, or child would contain three copies of this chromosome. Excess chromosomes and missing chromosomes are common in human conceptuses. Fortunately, mother nature usually ends abnormal pregnancies very early. That is why a 29 year old has a one in one thousand chance of having a child with Down’s syndrome while a forty year old’s chance is about one in one hundred.
In summary, everyone makes abnormal embryos. With PGS/PGD one may know whether up to ten pairs of chromosomes are normal or not. Over the years our pregnancy rate with PGS/PGD has always remained around 50% while the children born have demonstrated no genetic surprises regarding sex or other chromosomes tested. Please review the issue of genetic mosaicsm with Dr. Pabon or with the genetic counselor.
What if there are no normal pre-embryos available for transfer?
Patients must think ahead and understand that regardless of their age, there may be no normal pre-embryos available for transfer. Reproduction in humans can be inefficient. Humans make abnormal gametes all the time and this phenomenon usually results in a failed attempt at conception or a pregnancy loss. Sometimes the results of the pre-implantation genetic screening inform us that there is a pre-embryo of the sex desired by the patients but that the pre-embryo has also been found to have abnormalities in other chromosomes tested other than the sex chromosomes.
For more information on Pre-Implantation & Genetic Screening as it relates to Family Balancing & Sex Selection, please click here.
What if not all Pre-embryos have complete genetic results?
The Fluorescent In Situ Hybridization procedures that tag the chromosomes with colorful probes may not yield results for all the chromosomes tested. Sometimes we transfer normal appearing pre-embryos with some chromosomal results lacking. Dr. Pabon or the genetic counselors can explain this further.