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IVF: Why two-thirds of embryos produced by in vitro fertilization suddenly stop growing

New insights into why some IVF embryos fall into “developmental arrest” may help researchers create treatments that allow them to grow normally.


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June 30, 2022

Development of human embryo

Tong Guoqing (CC-BY 4.0)

About two-thirds of Embryo What is created during in vitro fertilization (IVF) mysteriously stops growing – and scientists may be beginning to understand why.

This finding gives some hints on how such embryos may one day be induced to develop normally. This can lead to higher IVF success rates. The treatment round that leads to pregnancy is about once every four times. In Europe.

In vitro fertilization involves placing some eggs in a dish containing sperm and checking them regularly under a microscope to see which eggs have been fertilized into embryos.

Some then develop into blastocysts, spheres of about 100 cells, which can be transferred to someone’s uterus. However, 6 out of 10 embryos do not reach the blastocyst stage. Instead, about 3 days after fertilization, it stops growing because it is composed of only a few cells.

It was a mystery why we stopped development Andrew Hutchins At the Southern Science and Technology University in Shenzhen, China.

For more information, the Hutchins team sequenced and investigated 17 arrested embryos. RNA, A strand of genetic material that indicates which gene is active.In the case of an active gene, the RNA molecule is the gene’s DNA As a template. RNA is then used as an indicator for making proteins.The team also examined the arrested embryos ChromosomeThe intracellular DNA package.

researcher This was combined with similar data on the other 6 arrested embryos. From previous studies, before comparing the entire set with existing RNA sequencing tasks in embryos that appear to be normally developing.

They were surprised to learn that arrested embryos do not have a higher incidence of chromosomal abnormalities than healthy embryos.

Instead, they found that the arrested embryos were divided into three groups. In type 1, the embryo makes the protein from the maternal RNA that was in the egg, but it cannot start making the protein from its own DNA. This is an important step in its development.

Type 2 and 3 arrested embryos cannot make a decisive transition to how to gain energy. Healthy embryos shift from oxygen-dependent metabolism to metabolism that requires little oxygen. This is because in very early pregnancies, the embryos implant in the uterus and their oxygen levels are low before the placenta develops.

In type 2 arrested embryos, their oxygen-dependent metabolism continues, but in type 3, it drops to low levels and neither properly transitions to non-oxygen-dependent metabolism.

In the second part of the experiment, Hutchins’ team attempted to treat a group of arrested embryos with antioxidant compounds such as resveratrol in red wine. “We basically force cells … to change the balance of their metabolism,” he says.

Resveratrol appears to have resumed development in about half of the 42 embryos arrested. However, most continued to stop growing and only three reached the blastocyst stage. And even these didn’t seem to have normal genetic activity, says Hutchins. “We’re forcing them to develop when they don’t really want it,” he says.

However, he says, the aberrant genetic activity may have been caused by the embryo being allowed to remain in the arrest stage for too long.

The findings are early work, but one day doctors say they may help reduce the number of embryos they initially arrest. Virginia Bolton At King’s College London. “It could increase the number of embryos available to a couple for pregnancy,” she says. “What they find is absolutely fascinating.”

Journal reference: PLoS Biology , DOI: 10.1371 / journal.pbio.3001682

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IVF: Why two-thirds of embryos produced by in vitro fertilization suddenly stop growing

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