Comprehensive Chromosomal Testing of Trophectoderm Biopsies of Blastocysts to Improve Live Birth Rates After in Vitro Fertilization: a Prospective Randomized Trial

The presence of chromosomal abnormalities (aneuploidy) in the pre-implantation embryonic stage is one of the major causes of human reproductive disorders, as it is responsible for embryo implantation failures, early or late miscarriages and the birth of children with chromosomal syndromes. This is mainly due to the existence of chromosomal abnormalities of meiotic, especially maternal, or mitotic origin occurring during the first three cell divisions of the embryo. As a result, human embryos have higher rates of aneuploidy than other species. Thus, it has been suggested that only 30% of conceptions reach term.

The objective of Assisted Reproductive Technologies (ART) is to optimize the chances of conception and delivery of healthy new-borns. It is necessary to improve the results of IVF (in vitro fertilization) programs and to reduce adverse effects (miscarriages, multiple pregnancies), especially in couples with patients with poor prognosis, such as older women. The choice of embryos to be transferred is a key step for the success of ART infertility treatments.

Currently, the choice of embryos is based solely on their morphology, evaluated on the 5th or 6th day of development at a stage known as the "blastocyst". Each embryo is observed under the microscope and described according to standardized morphological criteria. This description of the blastocyst is based on 3 constituents of the embryo: the degree of expansion of the blastocoelic cavity, the appearance of the internal cell mass (ICM) and the presence of trophectodermal cells (TE). These criteria have been described as predictive of live birth rates after transfer of fresh or thawed embryos. However, its ability to identify the embryo with the highest potential for implantation is debatable, due to its weak association with embryonic chromosomal status, which is a critical factor in the implant potential of each embryo. In addition, it is known that embryos that do not meet these morphological criteria are discarded, although it has been proven that their transfer could lead to a live birth.

Since the risk of embryonic aneuploidy is significantly increased after the age of 35, the objective of our RCT is to evaluate the efficacy of the CTTEB using the latest technologies and methodologies (i.e., combined embryo culture to blastocyst stage, immediate freezing of the embryonic cohort with delayed transfer, TE biopsy, NGS, and Single Embryo Transfer (SET)) in the management of infertile patients over 35 years of age. The live birth rate obtained after the first transfer of a single frozen embryo will be compared between two groups of couples, randomized in two arms: i) transfer of a single euploid blastocyst; ii) transfer of a single blastocyst of unknown chromosomal status, chosen on the basis of the usual morphological criteria, in the first thawing cycle following the freezing of all the blastocysts of the patient couples.

In addition, the culture medium of each embryo collected will be analysed in a second stage to assess whether it is possible to develop a diagnosis of aneuploidy without the need for trophectoderm biopsy (non invasive).