September 17, 2018
Fertility technologies can seem like a lesson in acronym-laden geek-speak, each new one more cryptic than the last. If you’ve heard of preimplantation genetic diagnosis (PGD) or preimplantation genetic screening (PGS), you know it’s true.
PGD and PGS, both collectively termed as preimplantation genetic testing, are performed prior to embryo transfer during an in vitro fertilisation (IVF) routine. While PGD is useful in ruling out hereditary problems, PGS can serve to eliminate the risk of structural or numerical chromosomal abnormalities. Both procedures are pointed at elevating the odds of a genetically healthy embryo. In a world where 1 in 20 babies is born with a genetic defect, preimplantation genetic testing can be a valuable tool, especially for couples of advanced age, or with a known genetic predisposition.
Here, we lift the lid on PGD and PGS.
Preimplantation Genetic Diagnosis
What is Preimplantation Genetic Diagnosis?
PGD is a reproductive technology, used in conjunction with IVF, to help identify genetic conditions prior to implantation. The process involves the maturation of embryos up to five days, followed by a biopsy of extracted cells from the resulting blastocyst. PGD is potent enough to trace up to 2,000 genetic disorders and is known to present 98% accuracy.
What Are the Advantages of Preimplantation Genetic Diagnosis?
PGD can be a valuable treatment for couples with a known family history of a single-gene (like sickle cell anaemia or cystic fibrosis) or sex-linked disease (like Fragile X syndrome or Duchenne muscular dystrophy). PGD is also a preferred option to determine a stem cell match for bone marrow transplants in siblings.
Preimplantation Genetic Screening
What is Preimplantation Genetic Screening?
PGS is a reproductive technology that screens embryos of chromosomally normal genetic parents. It is done with the intent of picking only those embryos with an optimum genetic profile (with a chromosomal count of 46). By discarding all others, the chances of a failed IVF cycle are minimised. The technique is performed in much the same way as PGD, with a biopsy being performed on the fifth day of embryo maturation. Embryos that exhibit a normal chromosomal structure are termed as ‘euploid’, all others, as ‘aneuploid’. PGS dramatically reduces the odds of IVF failure by ensuring the genetic integrity of the embryo prior to transfer.
What Are the Advantages of Preimplantation Genetic Screening?
Unfortunately, all couples are at risk of producing defective embryos, although the exact risk may vary from couple to couple, increasing in proportion with a woman’s age. A defective embryo is almost certain to result in implantation failure, with even the few that make it to implantation perishing in a biochemical pregnancy, miscarriage or stillbirth. PGS is a recommended option for couples with chronic male factor infertility, advanced age or repeated pregnancy loss. While PGS is gaining momentum among couples looking to shorten their lead time to conception, it does come with a handful of risks; the most significant being the chance of embryonic damage as a result of biopsy. Other risks include frozen embryo damage, genetic disorders beyond the PGS purview, and mosaicism, a term used to imply a genetic dichotomy, with some cells appearing healthy, others, not. In some cases, mosaicism can give rise to inaccurate test results. Another factor to consider is that while PGS can rule out chromosomal anomalies, it does not consider the compounded risk presented by environmental factors like toxins and pollutants, which could impact pregnancy.
Hitting the Genetic Jackpot: How to Go About Preimplantation Testing
Whatever your reason to undergo preimplantation genetic testing, it’s important to begin with a good fertility centre. An experienced fertility specialist can help you weigh the pros and cons of preimplantation screening or diagnosis, and guide you systematically through a treatment programme. When choosing a fertility doctor, invest time in first-hand research. Make a list of criteria that are important to you and shortlist fertility specialists that make the cut. Aside from personal factors, consider experience, success rates and feedback from fellow guests. By seeking the best expertise, you can maximise your chances right at the outset.