With improved success rates of assisted reproductive techniques like IVF, many fertility clinics have adopted implanting a single embryo during an IVF cycle, aimed at avoiding a multiple pregnancy. The complicated task of electing the best possible embryo to implant in a woman undergoing IVF treatment falls on an embryologist.
Clinical embryologists typically examine specific features of the embryos using a light microscope to determine the quality and viability of an embryo. According to Mumbai-based clinical embryologist Goral Gandhi, an early form of prenatal genetic diagnosis, Preimplantation Genetic Testing (PGT) helps the embryologists identify abnormal embryos.
Currently, PGD and PGS involve taking a cell from the in vitro embryo at the blastocyst stage. This cell is then biopsied and the DNA is examined. Data from preimplantation genetic testing for aneuploidy (PGT-A), a test of whether cells form the embryo at the blastocyst stage possess an abnormal or normal number of chromosomes, can also be used for the same purpose.
However, these crucial tests carry the risk of false negatives (which could lead to transferring an embryo with a chromosomal abnormality) and false positives (which could lead to discarding a normal embryo). “The procedure is invasive, and since only one cell is examined, the test cannot identify mosaicism in the embryo,” explains Dr Goral Gandhi.
Recent studies, however, have revealed that the DNA shed from early embryos hold the potential to provide an alternate way of genetically testing them, without having to do a biopsy. The new study is aimed at exploring whether the DNA shed by the embryo into its culture medium could be used. This could work in a similar way to Non-Invasive Prenatal Testing (NIPT), where foetal DNA can be removed from the mother’s bloodstream.
A pilot study that observed 115 blastocysts from 39 PGT-A (preimplantation genetic testing for aneuploidy) cycles revealed that the results were quite similar to those in case of NIPT. Some previous studies also compared the DNA obtained from cell biopsy with cell-free DNA from the embryo and found that the two methods returned similar results in as many as 80 percent of the samples.
Clinical embryologist Goral Gandhi from Mumbai is of the opinion that the primary challenges to the advancement of this procedure remain the maternal DNA contamination and the possibility of embryo mosaicism. “The question is whether this external DNA can be detected from the spent culture media,” Goral Gandhi says.
While some experts argue that this approach may lead to viable embryos being discarded unnecessarily, a number of embryologists are of the opinion that this technique, with further improvements, holds the potential to replace biopsy in the near future.