Blastulation rate is associated with cumulative sustained implantation after in vitro fertilization (ivf) and euploid frozen embryo transfer (fet)

To determine whether blastulation rate of an embryo cohort is associated with reproductive outcomes. This was a retrospective study of autologous first IVF cycles at a university-affiliated private practice from January 2020 to December 2021. All cycles that underwent IVF-ICSI with preimplantation genetic testing for aneuploidy (PGT-A) and had at least one single FET, were included. Only cycles with complete outcomes for the cohort were included, defined as achieving sustained implantation or exhausting all available embryos without success. Cycles with donor oocytes, surgically retrieved sperm, or endometrial thickness of < 7 mm at time of transfer were excluded. Sustained implantation was defined as an FET resulting in discharge of the patient at 8 weeks gestational age with an ongoing pregnancy. Cumulative sustained implantation rate was calculated as the percentage of embryo cohorts resulting in at least one ongoing pregnancy. Statistical analyses included one-way analysis of variance (ANOVA) and multivariate logistic regression. Adjusted odds ratios (aOR) for each outcome were calculated to account for potential confounders: patient age, body mass index (BMI), number of 2 pronuclei (2PN), euploidy rate, and embryo morphology. A total of 1,968 patients’ first IVF cycle embryo cohorts were included. The average patient age at time of retrieval was 35.7 ± 4.1 years and mean AMH level of 2.7 ± 2.6. The mean number of blastocysts per cohort was 4.9 ± 3.9 with a mean of 3.5 ± 3.1 euploid blastocysts per cycle after PGT-A. Cycles were subdivided into blastulation rate quartiles: first (<40.0%), second (40.0-53.7%), third (53.8-72.6%), and fourth quartile (72.7-100.0%). After adjusting for confounders, blastulation rate was not associated with sustained implantation of the first FET of the cohort (aOR vs lowest blastulation rate quartile: 0.98, 95% confidence interval [CI] 0.74 – 1.31; 0.92, 0.69 – 1.23; and 1.05, 0.78 – 1.41 for the second, third, and fourth blastulation rate quartiles, respectively). However, higher blastulation rate did correlate with higher rates of cumulative sustained implantation (aOR and 95%CI vs lowest blastulation rate quartile: 1.77, 1.22 – 2.55; 2.84, 1.87 – 4.29; 3.56, 2.36 – 5.35 for the second, third, and fourth blastulation rate quartiles, respectively). Higher blastulation rates of an embryo cohort of an autologous IVF cycle are associated with an increase in cumulative sustained implantation rates. However, this parameter does not correlate with the first transfer’s outcome in each cohort. A lower blastulation rate may represent an embryo cohort’s impaired metabolic state and result in worse FET outcomes. Other possible explanations include unidentified patient-related confounders and embryology laboratory conditions that may affect individual embryo cohorts.