Genetic testing methods like PGS and PGS when combined with IVF treatment reduce the possibility of passing on genetic diseases to the child, risk of recurring miscarriages, and also improve the odds of getting pregnant.
Both these genetic screening technologies require IVF and are different in the way they are used. Both these treatments also differ in their methods of application. They do not guarantee a healthy birth but can be helpful for those couples trying to get pregnant without much success. You can decide if PGS/PGD with IVF is suited for your family. But before that, you must understand the procedure, its impact, costs and risks associated with each of these technologies. Read on to find out more in detail about these genetic testing methods that are being used by fertility doctors to help couples have a healthy pregnancy.
What Is Preimplantation Genetic Screening (PGS)?
Preimplantation genetic screening (PGS) does not look for specific genes but the overall chromosomal makeup of the embryo. Embryos are classified into two types: euploidy and aneuploidy. Under normal circumstances, the egg and sperm both contribute 23 chromosomes each. Together, they create a healthy embryo with 46 chromosomes and this is what is called an aneuploid embryo.
In some cases, if an embryo happens to have an extra chromosome or misses one it is called aneuploidy. Aneuploidy embryos, in most cases, fail to implant or result in a miscarriage. In exceptional circumstances, it can result in pregnancy and birth, and the child born may be born with mental or physical disabilities. Down’s Syndrome is an example of an additional chromosome. PGS testing results can identify this prior to the embryo being transferred to the uterus. PGS can also determine the genetic gender of the embryo. Comprehensive Chromosome Screening (CCS) is a technique used in PGS that identifies whether the chromosome is XY ( male) or XX (female). This is done to avoid any particular gender-linked disorder or to balance family.
To Whom is PGS Recommended?
PGS is recommended to those parents who do not have a history of known genetic abnormalities. It is also recommended to patients who meet the below criteria:
- Couples who wish to know the sex of the baby.
- The female partner is over 38 years of age.
- Couples who are interested in single embryo transfer.
- Couples who have a history of miscarriages.
- Couples who have a record of failed IVF treatment or implantation.
Reasons for Considering Preimplantation Genetic Screening
Listed below are a few common reasons why PGS may be used with infertility treatment.
- It may improve the chances of success for a single embryo transfer.
With an elective single embryo transfer, doctors transfer just one healthy embryo through IVF. This improves the odds of pregnancy, reduces the risk of miscarriages and also the risk of multiple births, which can be a risk to the mother and babies.
2. To identify the gender of the baby.
PGS can help detect the gender of the baby and thereby reduce the risk of gender-based genetic diseases.
3. It may help lower the risk of miscarriage.
Miscarriage is common in 25% of pregnancies. Having recurrent miscarriages (three times in a row) is not a good sign. It could be detrimental to the mother’s health and also reduce the chances of getting pregnant. PGS helps to reduce the odds of having a miscarriage.
4. Increasing the chances of pregnancy through IVF
Fertility doctors recommend IVF to enhance the chances of getting pregnant especially where there is male infertility, repeated failed attempts of IVF implantation and women who are beyond maternal age. There are some clinics who offer PGS mandatorily with IVF to all patients.
PGS IVF Procedure
PGS testing for IVF is done in two methods. There are several methods to screen the presences of 24 chromosomes and it is called Comprehensive Chromosomal Screening ( CCS). The most common methods for CCS are Array-Comparative Genomic Hybridization ( aCGH) and Next-Generation Sequencing (NGS). Both these methods are performed on several cells on an embryo that is 5-6 days old. In some cases, it is done on some cells on embryos that are 3 days old too. The steps involved are performed by experts and laboratories:
- Embryos are produced with conventional IVF or intracytoplasmic sperm injection (ICSI) and these fertilized embryos are cultured for 3-5 days.
- Embryo biopsy is performed on the third or fifth day of development. On day 3, embryo biopsy involves removing one or two cells for testing.
- Once the biopsy of cells is completed, it is placed in test tubes and transported on the same day to reference laboratories for analysis.
- The cells are analysed to check for any inconsistencies.
- The results of the analysis take about 24 hours, so the embryos have to be frozen by a method called vitrification.
- Finally, the embryos are thawed. A single embryo with a normal PGS result is picked and the embryo is transferred back into the uterus in the subsequent IVF procedure.
Cost of PGS
Different clinics charge different rates for PGS treatment. The cost of PGS treatment is over and above the cost of IVF treatment. Typically, PGS treatment will cost about $3000 -$5000 in addition to the IVF treatment. Each clinic will differ in their charges depending on the number of embryos they test. Over and above, you may also need to pay for the frozen embryo transfer cycle too.
The PGS normal embryo success rate in combination with IVF treatment depends on the result of the number of embryos produced in the IVF cycle. As per research, there is a 60%-80% chance of a live birth rate when the chosen frozen embryo is transferred in an IVF cycle. This data has a positive bearing on women who undergo PGS and IVF and are over maternal age, at risk of miscarriages and have had previous IVF failure. There is always a chance of no embryos being suitable for transfer to the womb for the following reasons:
- Failure to produce enough eggs or less unfertilized eggs.
- Damage to the embryos while removing the cells.
- All the embryos are aneuploid.
What Is Preimplantation Genetic Diagnosis (PGD)?
PGD is more of a diagnosis. PGD is used to identify a specific disease or a set of genetic diseases in an embryo. This is to avoid passing on the genetic disease. There are times when both PGD and PGS are needed. It can also be done when a couple has a genetic disease and they do not want to pass it on to the child. PGD does not test one single embryo for all possible diseases. It tests for one specific disease and does not tell you any other possible genetic diseases that could be present. PGD is suited for anyone who knows they are at risk of passing a chromosome abnormality or genetic disease to the child. Through this process, the laboratory determines the embryos that are unaffected and suitable for uterine transfer. Couples opting for PGD also conduct genetic tests like amniocentesis and chorionic villus sampling during pregnancy.
To Whom Is PGD Recommended?
PGD is recommended to couples who have a particular genetic tendency. It is done to ascertain the probability of passing on the abnormality. The following are those who could get it done:
- Couple with a family history of aneuploidy (imbalance in a number of chromosomes) resulting in miscarriage, Down’s syndrome, and birth defects.
- Families with single-gene defects like sickle cell, anaemia, muscular dystrophy, and cystic fibrosis.
Reasons Why Preimplantation Genetic Diagnosis Maybe Recommended
The possible reasons why a doctor may recommend PGD are:
- To prevent the specific genetic disease from getting passed on to the baby.
The most common reason is to determine the likelihood of whether a genetic disease is likely to be passed on to the child.
2. To detect abnormalities in the embryos.
PGD is useful to detect abnormalities in chromosome numbers, translocations, hereditary cancer and genetic mutations.
- For gender selection.
Many couples choose to use PGD to select the gender of their child.
PGD IVF Procedure
PGD is performed during the IVF procedure. Eggs are fertilized in a petri-dish and placed in a special incubator. Eggs grow for up to 5-7 days until they reach the size of hundred cells which is called a blastocyst. At this stage, doctors perform ‘trophectoderm biopsy’ by removing cells from the area which forms the placenta (cells developing into the foetus are not used in PGD). The embryo is held under a microscope using a pipette. A hole is created in the shell around the embryo using a laser and another pipette draws out a few cells away from the embryo. While doctors perform genetic testing on the extracted cells, the embryos are frozen. Doctors carry a genetic probe based on the genes of the parents and the disease they carry. This probe is then used on the biopsied cells to locate the embryos which have the disease, may carry it or are normal. Normal embryos are thawed and transferred to the uterus to complete the IVF procedure.
Cost of PGD
PGD costs about $3000-$5000 over the IVF treatment which costs $12,000.The PGD cost includes the fertility boosting medications and it increases the total cost of the treatment by a few thousand dollars. The costs vary according to the type of tests and the number of tests performed. Some insurance companies may cover the cost of the treatment.
PGD is able to diagnose the presence of genetic defects and the accuracy is up to 98% in most cases. Post undergoing PGD, prenatal testing like amniocentesis and chorionic villus sampling (CVS) will be recommended to confirm the results of PGD diagnosis. The revelation of genetic defects prior to pregnancy reduces the risk of a foetus being affected significantly.
Difference Between Genetic Testing and PGD/PGS Testing
- PGS and PGD testing take place during preimplantation. Prenatal testing is done when implantation has occurred and is done once pregnancy is established.
- CVS and amniocentesis identify chromosomal abnormalities in the unborn foetus letting the couple decide whether they wish to terminate the pregnancy.
- PGS and PGD are not final determinants of the existence of genetic defects. Doctors, very often, recommend prenatal testing in addition to PGS/PGD in case there is an error.
Risks Involved With PGS/PGD Testing
Any IVF treatment involving PGS and PGD comes with the associated risk of conventional IVF treatment. There are additional risks involved for those considering PGD/PGS:
- Birth rates will not be similar to those of age-similar peers. The main reason being some embryos may not survive the process and some may come back with negative results.
- Biopsy done on day 5 embryos carries the risk of identical twinning.
- The chances of errors are more. Embryos tested as abnormal may be ‘normal’ and vice versa. This could result in healthy embryos being discarded.
- If all the embryos test negative then there will be no transfer resulting in loss of money, time and mental trauma.
- Vitrification and thawing can lead to the loss of healthy embryos.
- A few healthy embryos may not stay alive until day 5, when the eggs are retrieved.
- Conducting biopsy on day 3 of the embryos may lead to the embryos not developing.
- PGD/PGS is not a guaranteed success. A child may still be born with genetic diseases which are why doctors recommend prenatal testing in addition to PGS/PGD for additional assurance.
- Both PGS/PGD testing along with prenatal tests do not guarantee a baby with no physical or mental disability.
- PGS aids in reducing the odds of a miscarriage but there is still an element of risk involved.
- The wait for results and the need to make a decision about embryos that come with inconsistent results can be emotionally draining.
- The technology is relatively new and we do not know what long-term effect PGS/PGD and IVF treatment can have on children post their birth.
Genetic screening tests have made families with genetic disorders or chromosomal translocations get a better chance of having a healthy baby. It has also helped the lives of doctors by helping them select healthy embryos. By reducing the chances of miscarriage and the chance of a healthier baby, these assistive technologies are helping the lives of many childless couples and bringing a ray of hope in their lives.