Preimplantation genetic testing for aneuploidy (PGT-A, PGS) detects chromosome copy number abnormalities of embryos and is an effective method for selecting the best embryos. It helps to achieve better pregnancy results by selecting embryos with normal chromosomes for transfer. The method is particularly beneficial for women over 35 years old and patients with recurrent miscarriages or several unsuccessful fertility treatments. In general, transferring embryos with normal chromosomes produces better treatment results regardless of the woman’s age.
Out of a young woman’s normal looking embryos, 40–50% may have an abnormal number of chromosomes in a cell, i.e. be aneuploid, while for women over 40 this figure may be as high as 75–90%. The majority of chromosomal abnormalities lead to arrested development of the embryo or an early miscarriage. However, variation between patients is high, and unsuccessful treatments are not necessarily a result of chromosomal problems.
Source: US CDC/SART (left), Harton et al. (2013) Fertility and Sterility 106:1695-703 (right)
How is preimplantation genetic screening and testing done?
In a PGT-A treatment, a sample of approximately 5-8 cells is taken from five- to six-day-old embryos and the embryos are frozen by vitrification. According to the analysis results, chromosomally normal embryos can be thawed and transferred to the uterus. Embryo chromosome testing can be used for selecting embryos with the best pregnancy prognosis reducing the number of failed embryo transfers. The pregnancy prognosis for a chromosomally normal embryo is at the best around 50 % and the risk of miscarriage is low.
By taking a few cells from the embryo to analyze the DNA there is a small risk of embryo damage which may impair embryo viability. An alternative method that avoids this risk is the non-invasive chromosome testing (niPGT-A, Non-Invasive Preimplantation Genetic Testing for Aneuploidy) which is based on analyzing the DNA secreted by the embryo into its culture medium.
In PGT-A treatments, embryos are cultured in the EmbryoScope®, an incubator with a monitoring device facilitating improved embryo selection. Ask us for more details about Ovumia’s PGT-A embryo selection.
