Are pregnancy rates affected by day of blastocyst cryopreservation in single euploid frozen embryo transfer cycles?

Abstract

There is inconclusive evidence whether day of cryopreservation of euploid embryos affects pregnancy rates. We sought to compare pregnancy outcomes between euploid blastocyst embryos cryopreserved on either day 5 or 6. Retrospective cohort study. 126 cycles performed at a large university-based center during a period of January 2013 through December 2016 were evaluated. Euploid embryos cryopreserved on either day 5 (n=77) or day 6 (n=51) and utilized in a single frozen embryo transfer (FET) cycle were included for analysis. Preimplantation genetic screening was performed by either array Comparative Genomic Hybridization or Next-Generation Sequencing. Only high quality blastocyst embryos were biopsied and frozen. The primary outcome was ongoing pregnancy rate (OPR). Secondary outcomes included implantation rate (IR), clinical pregnancy rate (CPR), clinical loss rate (CLR) and multiple gestation rate (MGR). Student’s t-test and Mann-Whitney test were used to assess continuous variables depending on how the data was distributed. Chi-square was used to assess categorical variables. Multivariate logistical regression was performed to control for potential confounding variables. A p-value <0.05 was considered statistically significant. No significant differences were noted between the groups for age (35.5±4.3 vs. 35.5±4.0), BMI (25.8±5.8 vs. 25.2±4.6), AMH level (3.1±2.3 vs. 3.6±4.4), previous live birth (37.7% vs. 49.0%), diagnosis of recurrent pregnancy loss (RPL) (23% vs. 14%) and number of prior FET cycles (0.3±0.7 vs. 0.6±0.9). There were no differences in pregnancy outcomes between the two groups (Table). Using bivariate analysis there was no difference in OPR between the two groups (OR: 0.84, 95% CI 0.40 - 1.73, p=0.63). A multivariate regression analysis was performed to control for the potential confounding variables of age, BMI, previous live birth, diagnosis of RPL, or prior FET resulting in an adjusted odds ratio for OPR of 0.78 (95% CI 0.37 - 1.65, p=0.51). Day of cryopreservation does not affect pregnancy outcomes in single euploid blastocyst transfers. Rate of multiples remains low in single embryo transfer cycles.Tabled 1Pregnancy OutcomesDay 5Day 6p-valueIR, n (%)55/77 (71.4)36/51 (70.6)nsCPR, n (%)53/77 (68.8)35/51 (68.6)nsOPR, n (%)45/77 (58.4)32/51 (62.7)nsCLR, n (%)8/53 (15.1)3/35 (8.6)nsMGR, n (%)1/53 (1.9)2/35 (5.7)nsns=not significant Open table in a new tab