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Preimplantation genetic testing (PGT): embryo biopsy associated with a small increase in risk of premature birth, new study suggests.

Embryo biopsy, the process of removing a few cells from the developing embryo in the IVF lab, is necessary to perform a genetic examination, prior to embryo transfer. How do embryos respond to biopsies and how do pregnancies continue?

Despite various debates on its potential benefits, preimplantation genetic testing is gaining widespread use. Not only it can help with the diagnosis of genetic disease in embryos, it may also provide a diagnosis of chromosomal abnormalities in embryos, the commonest reason of failed implantation and miscarriage in pregnancy.

As embryo biopsy involves removing some cells from the developing embryo in the IVF lab, it is important to examine the consequences this process may have in implantation and the pregnancy which follows. PGT in IVF programs has been around for almost 3 decades. However, it is only in recent years that PGT has been used in such a scale that we can collect more information on this issue.

The timing of embryo biopsy is the first factor which was found to affect the developing embryo in the IVF lab. Although in practice for many years, embryo biopsy at the cleavage stage, when the embryo starts to divide around the 3rd day of its life, is now largely abandoned, as it was found to reduce the chance of the embryo implanting successfully. The majority of embryology labs have now moved to biopsies at the stage of blastocyst, removing a few cells from the outer surface, an area which is destined to form the placenta in pregnancy. The biopsy of the embryo at the stage of blastocyst is considered safe, as no differences were seen in chance of pregnancy in previous studies. However, it is important to note that the experience of the operator, with regards to amount of cells removed, is highly important. Removing too many cells and the chance of pregnancy following embryo transfer is reduced with pregnancies ending in miscarriage more often.

As embryo biopsies involve the forming placenta, it is becoming a priority to focus on placental function during the pregnancy. A dysfunctional placenta may result at lower birth weight, increased risk of high blood pressure and premature birth.

A previous study published in Fertility and Sterility Journal in 2019, found an increased risk of high blood pressure in pregnant women following IVF and PGT, although the number of pregnancies examined was small. Now, new research, based on a large national database from the U.S., in the most extensive study by now, is shedding more light in this highly important issue of embryo biopsy consequences on pregnancy. The study, published in the American Journal of Obstetrics and Gynecology, examined the course of over 16000 pregnancies following frozen embryo transfer cycles and compared pregnancies after PGT with pregnancies without. No effect from the embryo biopsy was observed in birthweight, however, a small increase in the risk of premature birth was documented in pregnancies following PGT.

It is becoming clear that further monitoring of pregnancies following an embryo biopsy for PGT is needed. As the potential benefits from genetic diagnosis at an early stage, prior to embryotransfer, have dominated public discussion, it is now time to extend our interests not only in embryo selection, but also in the course of the pregnancy itself. Although the increase of risk of premature birth appeared only modest, we should not underestimate the significance this may have in some pregnancies, as baby health issues because of prematurity can linger for quite a while.

©2021, Nicholas Christoforidis, Fertility Matters
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