Should single embryo transfer be used in patients with any kind of infertility factor? Preliminary outcomes

Multiple embryos have been transferred to compensate for low implantation rates, which in turn, increase the likelihood of multiple pregnancies. Despite the publication of clinical guidelines and a reduction in the number of embryos transferred, double embryo transfer still is the most common practice. There is no clear evidence of who should receive the single embryo transfer (SET), and it is more commonly indicated for patients of good prognosis. However, it is not clear how much the presence of other infertility factors can affect the SET prognosis. The aim of this study was to evaluate differences in clinical pregnancy rates (CPR) of frozen-thawed SET cycles for women presenting with different infertility factors.

Retrospective cohort study evaluating 305 frozen-thawed SET cycles performed in the last 10 years in a private IVF center. We included patients undergoing ovarian stimulation cycles, using ejaculated sperm and a frozen-thawed ET. Embryos were routinely vitrified and warmed up, and the blastocysts were transferred after endometrium preparation. The cycles were categorized according to the infertility factor classified by the Society for Assisted Reproductive Technologies (SART) as anatomic female factor (n=55), endocrine female factor (n=26), endometriosis (n=37), male factor (n=60), ovarian insufficiency (n=26), unexplained (n=24), multiple factors (n=45) and other (n=32). CPR were compared between the groups and the multivariate analysis was performed to evaluate the association of each infertility factor and the CPR, adjusted for confounders.

The women varied in age from 18 to 44 years (35.9±3.8), presented Body Mass Index of 22.4±3.1kg/m², baseline serum FSH of 7.4±8.3 IU/ml, and had a mean of 11.0±8.4 MII oocytes recovered and 6.4±5.3 embryos cryopreserved. The CPR, according to infertility factors were: anatomic female factor (25.9%), endocrine female factor (30.8%), endometriosis (27.8%), male factor (20.7%), ovarian insufficiency (21.7%), unexplained (9.5%), multiple factors (17.1%) and other (20.7%). Multivariate analysis did not show significant association of infertility factors and CPR adjusted for confounders.

Patients presenting different infertility factors seem to have a satisfactory CPR for a SET cycle, except those with unexplained infertility. This is a preliminary outcome and the number of patients by category is small; in addition, the retrospective characteristics of the study are its limitations. Overall, our findings suggest that patients presenting any infertility factor, except unexplained infertility, are suitable to receive a SET with satisfactory outcomes.