If you’re having fertility treatment, you’ll want to make sure the chances of conception are as high as possible. As a result, a common question many women ask when undergoing IVF treatment is how doctors select the best embryo. Until recently, this was based on morphology – which simply put, is how the embryo looks under the microscope. However, now, doctors have developed a test to assess the genetics of an embryo. This test is known as preimplantation genetic screening or PGS. The test is also called preimplantation genetic testing for aneuploidy or PGT-A. Through identifying the best quality embryos, this test can improve success rates with chromosomally normal embryos. What Does ‘Chromosomally Normal’ Mean? Before going into exactly how PGS works, it’s useful to discuss why you might want to consider adding the test to your IVF treatment. Essentially, PGS can help doctors select a chromosomally normal, high-quality embryo to implant into the uterus. Chromosomes are the containers that carry our genetic information or DNA. When doctors say ‘chromosomally normal’, what they are referring to are embryos with the complete set of 46 chromosomes required to grow a healthy baby. If an embryo has any deviation from 46 chromosomes – whether there is an extra or missing chromosome – it will be likely to result in a failed implantation, biochemical pregnancy, miscarriage, or a pregnancy affected by a chromosomal syndrome. While women of any age are at risk of producing embryos with chromosomal imbalances, the risk increases as the egg source ages. This is why women who have babies later in lifeare more likely to have a pregnancy with a chromosomal imbalance. It’s for this reason that older women may wish to include PGS as part of their IVF treatment. However, PGS is available to patients of any age. So What is PGS Exactly? In the past, fertility specialists would transfer an embryo into the uterus three days after fertilization. Now, research has shown that success rates with chromosomally normal embryos improve if they transfer a few days later. Now, doctors generally transfer the embryo at around five or six days into development, at blastocyst stage. Not only does this improve viability, but it also gives doctors the opportunity to perform a biopsy with a low risk of embryo arrest. The embryo biopsy can be utilized to perform preimplantation genetic screening or PGS. This test can identify chromosomally normal embryos, which increase the chances of a healthy pregnancy. To perform the biopsy, an embryologist removes 2-10 cells from the precursor placenta cells of the blastocyst embryo, called the trophectoderm. These outer cells are what eventually will become the placenta. It’s important to know that the inner ball of cells, called the inner cell mass – which are what will grow into your baby – are not biopsied in this procedure. How Do These Tests Improve My Chances of Conceiving? As we’ve covered above, PGS helps doctors select a chromosomally normal embryo to transfer to the uterus. PGS improves success rates because chromosomally normal embryos are much more likely to implant and result in pregnancy. Furthermore, PGS also reduces the chances of miscarriage, as the most common cause is chromosome abnormality. Is There Evidence About Success Rates with Chromosomally Normal Embryos? Yes – a study conducted by the Colorado Center for Reproductive Medicine found that women ages 38-42 had a similar live birth rate to women 37 or younger if a chromosomally normal embryo was transferred. The study found that women with advanced maternal age (ages 38-42) had a chromosomal error rate of about 62% compared to women under 38 who had a chromosomal error rate of 37%. Women in both age groups had frozen embryo transfers of chromosomally normal embryos and the live birth rates were very similar for both groups – 60% live birth rate for women 38-42 and 64% live birth rate for women under 38 years. If It’s So Effective, Why Doesn’t Everyone Do It? Every IVF case is unique – therefore, some women may choose to not include PGS in their treatment. PGS can be an expensive addition to the costs already associated with IVF. Considering that the process isn’t 100% accurate – currently, accuracy rates sit at around 98% – some people decide against making the investment. Moreover, as the research we mention infers, PGS does not majorly impact implantation success in every case. As with all IVF treatment, even with PGS the top success rates with chromosomally normal embryos does not exceed 60–70%. Your IVF Treatment is Your Journey Everyone’s IVF journey is completely unique to them. Your fertility doctor will make special recommendations depending on you and your partner’s circumstances. Therefore, before making any decisions about your treatment, carefully consult with a health professional and gather as much research as you can. With the right information, you can make sure you go into your fertility treatment feeling informed and empowered.