Medical Technology

Commonly Discarded Mosaic Embryos Might cause Live Births

(Reuters Health) The majority of human embryos that were discarded prior to implant could be used in an in vitro fertilization method that could result in a live birth. This is according to a recent study.

Researchers studied the distribution and prevalence of aneuploid cells in unselected preimplantation embryos. They disaggregated 73 blastocysts down to five sections, including the inner cell mass (ICM) and four trophectoderm (TE) biopsies, to determine how abnormal cells are dispersed throughout the embryo.

The researchers found that mosaicism impacted less than 50% of embryo cells in one TE biopsy. This indicates moderate to low mosaicism. Only 1percent of aneuploidies showed an impact on other parts of the embryo.

“We discovered abnormal cells are restricted to a tiny portion of the trophectoderm. They do not affect other TE sections or the entire cell mass,” said lead author Antonio Capalbo, a clinical geneticist and embryologist and scientific director at Igenomix Italy in Vicenza.

“This is not surprising since some mosaicism that is low can be a normal feature of developing placental cells , and they are likely to be well tolerated in this tissue,” Capalbo said by email.

Capalbo stated that a possible alternative explanation is that mosaicism-consistent results in a TE biopsy may be due to technical variations. This could be due to the well-known experimental noise that results from single cell analysis. Capalbo said that both explanations are valid reasons for why these embryos have same reproductive capacity as fully euploid embryos.

The primary outcome of the study was live birth rate. The secondary outcome was miscarriage rates.

Overall, researchers found that in 484 euploids, 282 low-grade mosaic, as well as 131 medium-grade mosaic embryos the rates of live births and miscarriages were comparable as were obstetrical and neonatal outcomes.

Capalbo stated that the evidence suggests that these embryos are identical in terms of reproductive capability and don’t increase the risk of chromosomal anomalies, including mosaicism, in the fetus or newborns.

It’s not entirely clear, however, whether aneuploid cells stop growing and become apoptotic or senescent or are precursors to placental mosaicism. The study team notes in American Journal of Human Genetics.

Capalbo stated that even though the results aren’t conclusive, they will allow doctors and patients to make better choices about the transfer of potentially mosaic embryos.

Capalbo stated that it was reasonable for genetic laboratories to cease reporting findings that are not of clinical significance to patients. “In clinical genetics, there is a widespread agreement that genomic findings should be reported only if they bring clear elements of clinical validity and value.”

SOURCE: American Journal of Human Genetics, online November 18, 2021.

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