IVF study sheds new light on early stages of embryo development

Amazing stuff! Looks like we still have to learn a lot more about the early stages of embryos. Still a long way to an artificial womb.

"By genetically testing nearly 1,000 embryos, scientists have provided the most-detailed analysis of embryo fate following human in vitro fertilization.

Nearly half the embryos studied underwent developmental arrest because of genetic mishaps in early development—a revealing insight that suggests more IVF babies could come to term with changes in the fertility treatment process. The unique combination of data from arrested embryos also sheds new light on the still largely mysterious earliest stages of pregnancy through natural means. ..."

From the abstract:

Background

The high incidence of aneuploidy in early human development, arising either from errors in meiosis or postzygotic mitosis, is the primary cause of pregnancy loss, miscarriage, and stillbirth following natural conception as well as in vitro fertilization (IVF). Preimplantation genetic testing for aneuploidy (PGT-A) has confirmed the prevalence of meiotic and mitotic aneuploidies among blastocyst-stage IVF embryos that are candidates for transfer. However, only about half of normally fertilized embryos develop to the blastocyst stage in vitro, while the others arrest at cleavage to late morula or early blastocyst stages.

Methods

To achieve a more complete view of the impacts of aneuploidy, we applied low-coverage sequencing-based PGT-A to a large series (n = 909) of arrested embryos and trophectoderm biopsies. We then correlated observed aneuploidies with abnormalities of the first two cleavage divisions using time-lapse imaging (n = 843).

Results

The combined incidence of meiotic and mitotic aneuploidies was strongly associated with blastocyst morphological grading, with the proportion ranging from 20 to 90% for the highest to lowest grades, respectively. In contrast, the incidence of aneuploidy among arrested embryos was exceptionally high (94%), dominated by mitotic aneuploidies affecting multiple chromosomes. In turn, these mitotic aneuploidies were strongly associated with abnormal cleavage divisions, such that 51% of abnormally dividing embryos possessed mitotic aneuploidies compared to only 23% of normally dividing embryos.

Conclusions

We conclude that the combination of meiotic and mitotic aneuploidies drives arrest of human embryos in vitro, as development increasingly relies on embryonic gene expression at the blastocyst stage.

IVF study sheds new light on early stages of embryo development | Hub

Meiotic and mitotic aneuploidies drive arrest of in vitro fertilized human preimplantation embryos (open access)

Fig. 1 Developmental outcomes of 1232 normally fertilized (2PN) embryos and their associated PGT-A results.