Biochemical pregnancy loss (BPL) is a very frequent issue in human reproduction. After the implantation of the embryo, hCG disappears very soon from the maternal bloodstream and no evidence of a clinical pregnancy is seen. Different studies showed that factors such as age, oocyte and embryo quality, and endometrium receptivity may have something to do with the occurrence of biochemical pregnancy loss post assisted reproduction treatment.

The main aim of this study is to evaluate the incidence of biochemical pregnancy loss (BPL) in three different cohort populations; patients undergoing frozen embryo transfer (FET) from own oocytes after preimplantation genetic testing for aneuploidy (PGT-A), patients undergoing FET from own and donated oocytes and with endometrial receptivity array (ERA), and patients undergoing FET from own or donated oocytes (without PGTA or ERA test).

We will analyse the incidence of BPL in these populations and try to determine the role of the euploid status embryo in the first group, the endometrium in the second group and the third one as control group. We are waiting to find the value of both players in the origin of BPL.

Human embryo implantation is a poorly understood process. Once the embryo implants in the endometrium, it starts to secrete hCG that can be measured in the maternal blood as early as 9 days after implantation. Only a minimal number of pregnancies get to newborn, and the majority are lost before reach the first trimester (Larsen et al., 2013).

We are looking for the role of the embryo after controlling its chromosomal ploidy, and the endometrium after controlling its transcriptomic expression. We will also use a no exposed group to the controlled euploid embryo factor neither endometrial factor that is the oocyte donation group. This analysis expects to provide more information about the key role of embryo or endometrium in BPL.

Inclusion Criteria:

Patients with the following selection criteria:

• IVF/ICSI patients aged between 18 and 44
• BMI 18-30 kg/m2
• Frozen embryo transfer from own oocytes after PGT-A
• Frozen embryo transfer with ERA test (from own or donated oocytes)
• Frozen embryo transfer (from own or donated oocytes)
• Single embryo transfer (SET) in all cycles
• Patients without uterine malformations
• Patients without recurrent miscarriage (≥ 3)
• Patients with adequate endometrial thickness (> 7mm)
• Patients without thyroid autoimmunity
• Patients without thrombophilia
• Exclude cycles with exclusively PGT-M
• Exclude FET in ovarian stimulated cycles

Exclusion Criteria:

Exclude cycles with exclusively PGT-M Exclude FET in ovarian stimulated cycles

-

Infertile patients who come to participating centres for assisted reproduction treatments. Patients will be divided into 4 groups according to the treatment carried out: PGT-A, ERA, FET from own oocytes (CO) or FET from donated oocytes (CD).