Reproductive potential of double inner-cell mass embryos: a case series and matched analysis in single euploid blastocyst transfers

Standardization of PGT-A and elective transfer of single euploid embryos (SEET) have significantly reduced twin pregnancy outcome after ART treatment. However, the presence of monozygotic splitting (MZS) after SEET remains a possibility. Recent research about factors associated with MZS has focused on the presence of two inner cell masses (ICM) within the same blast. Yet, due to limited information, more clinical data about the reproductive potential of “double-ICM” transfers is required We analyzed patients who underwent IVF/PGT-A between 2016 and 2023. Only patients who underwent a single euploid FET with endometrial preparation were included. At the time FET, blastocysts were morphologically graded, and cohorts were selected based on the presence of a double ICM. IVF outcomes of these cohorts were compared with those of a control population consisting of normal ICM embryos. Controls were selected from a propensity score matched 10:1 population, matched by patient age, body BMI, AMH, endometrial thickness at FET, and year of treatment. Patient demographics and FET outcomes were analyzed and compared between the two groups using T-test, U-test and χ2 tests. A two-sided P value of < 0.05 was considered significant 18 FETs with double ICM embryos were analyzed, 17 (94.4%) had a positive pregnancy test. Of these 17, 7 (41.2%) experienced a biochemical pregnancy loss, while 10 continued to a clinical pregnancy (58.8%). Out of the 10 clinical pregnancies, all were carried to term, with 2 patients delivering twins (20%) and the rest delivering singletons (80%). In one case, 2 gestational sacs were present during early pregnancy scans, but one of the sacs was absorbed early and the other sustained development until the patient delivered one healthy baby. In 2 other cases, monochorionic diamniotic twins were observed and both pregnancies continued to delivery. A sub analysis was conducted comparing 179 matched control SEET cycles. There were no significant differences in oocyte age, age at FET, BMI, day 3 FSH, endometrial thickness, and previous euploid embryo transfers between cohorts. However, the double ICM FETs had significantly higher positive pregnancy test rate (94.4% vs 73.2%, p=0.04) and comparable implantation (55.5% vs. 60.8%, p=0.65); clinical pregnancy (55.5% vs 58.6%, p=0.04); and live birth rates (64.4% vs 47.4%, p=0.62) compared with normal ICM FETs. Furthermore, Double ICM embryos had significantly higher biochemical pregnancy loss (41.2% vs 16.8%, p=0.01) and multiple pregnancy rates (20% vs 1.2%, p=0.002). An objective assessment of the characteristics of the ICM, beyond the standard grading system, should be implemented as a standard of care. Our study findings suggest that double ICM euploid embryos have a higher risk of biochemical pregnancy loss and monozygotic splitting, but similar implantation, clinical pregnancy and live birth rates compared to single ICM embryos