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Common technique used in IVF impacts placenta growth and function

last modified Jan 17, 2020 01:35 PM
New mouse study by the Watson group published in Reproduction shows that a common technique required for in vitro fertilization changes how genes are expressed in the placenta and alters fetal and placental growth with potential implications on life-long health.

Assisted reproduction technologies (ARTs), like IVF, have helped many people around the world to have babies. It is predicted that over seven million babies have been born using some form of ART. While it is generally safe, growing evidence suggests that individuals born using these technologies are at an increased risk for complications during pregnancy and even cardiovascular disease later in life. Given the extent to which these technologies are used, it is important to understand how they influence fetal and placental development.

In this study, the researchers show that simply transferring a mouse embryo from its biological mother to a new mother affects how genes important for placenta development are expressed. The placentas were smaller than expected and were associated with fetuses that were of normal size or even larger than controls. This means that the change in gene expression was an adaptive response to improve the function of the placenta to maintain fetal growth. Whether this adaptive response can be maintained until the end of gestation to result in a normal baby is unknown.

How ‘embryo transfer’ changes gene expression remains unclear, though the researchers looked into epigenetic mechanisms. Epigenetics is an additional layer of instructions that lies on top of DNA (for example, DNA methylation) and controls whether a gene is turned ‘on’ or ‘off’. This study found that some genes that were misexpressed had normal DNA methylation patterns or were not associated with control regions that would normally contain DNA methylation. Therefore, different types of molecules involved in epigenetic control of gene expression (for example, histone methylation) should be assessed.

This type of ‘embryo transfer’ technique is commonly used in ARTs in humans, whether it is placing a donor embryo into a woman’s uterus or an embryo back into its biological mother. While we do not know whether the effects of embryo transfer in mouse will carry over to humans, the implications are clear. It is fairly well established that adverse changes in placenta development and function can affect the success of a pregnancy and the health of an individual later in life.

Reference: Katerina Menelaou, Malwina Prater, Simon J. Tunster, Georgina E.T. Blake, Colleen Geary Joo, James C. Cross, Russell S. Hamilton and Erica D. Watson (2020), Blastocyst transfer in mice alters the placental transcriptome and growth. Reproduction 159(2): 115-132. https://doi.org/10.1530/REP-19-0293

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