JBRA Assist. Reprod. 2025;29(Suppl 1):5-5
ORAL PRESENTATION
doi: 10.5935/1518-0557.20250063
1Fertilab. Buenos Aires, Argentina
2Universidad de Tres de Febrero. Buenos Aires, Argentina
3IBYME-CONICET. Buenos Aires, Argentina
Objective: To evaluate the association between blastocoel expansion at devitrification/warming and transfer, and ART outcomes of clinical pregnancy (CP), live birth (LB) and miscarriage (M) in single vitrified/warmed blastocyst transfer cycles.
Methods: This retrospective observational cohort study includes single vitrified/warmed blastocyst transfer cycles performed at Fertilab in 2023. Blastocysts were obtained in ICSI cycles. Morphological grading was 3 or 4, AA-AB-BA-BB (Gardner criteria). Blastocysts were vitrified/devitrified using a commercial kit (Kitazato/Cryotop) following standardized procedures. All embryos were devitrified/warmed in the morning using Global Total LP medium, with transfer times varying depending on doctor and patient preferences as well as availability (45 min-6 h). Blastocoel expansion was subjectively assessed (Expanded=E; Collapsed=C) upon devitrification (E1,C1) and prior to transfer (E2,C2). Expanded blastocysts included 70-100% expansion; in Collapsed blastocysts the blastocoel was not visible. Four groups were defined after evaluation by 2 experienced embryologists: E1E2, C1E2, E1C2 and C1C2. Patients were followed until delivery. Outcomes evaluated: 1) CP (visualization of a gestational sac), 2) LB (birth of a live infant ≥24 weeks of gestation) and 3) M (non-viable pregnancy after confirmation of intrauterine pregnancy on ultrasound scan). Outcomes were expressed as rates (percentage) per transfer (CPR; LBR; MR). Cycles that resulted in biochemical pregnancies were not included in the study.
Results: 1) 80% (415/521) of total blastocysts were classified as E (E1E2=64%, C1E2=36%) while the remaining 20% (106/521) were classified as C (C1C2=74%; E1C2=26%). 2) Total CPR was 34% (178/521). Differences (p=0.0005) in CPR were found between E embryo transfer (Et: 38%; 158/415) and C embryo transfer (Ct: 19%; 20/106). Similar trends were found in subsets of a) patients oocytes (CPR: 39% for Et and 23% for Ct; p=0.03), b) donor oocytes (CPR: 37% for Et and 14% for Ct; p=0.005), c) patients grouped by age, both in young women (CPR women≤35y.o.: 37% for Et and 16% for Ct; p=0.004) and older women (CPR women>35y.o.: 41% for Et and 20% for Ct; p=0.005), d) in embryos with >2h of culture (Et=36%, Ct=15%; p<0.0001). 3) In the total population, LBR was 29%, with higher (p=0.0005) rates in Et (33%; 136/415) than in Ct (16%; 17/106). 4) In patients that achieved a CP, the chance to give birth or have a miscarriage was similar when E or C blastocysts were transferred (LBR: Et=86%, 136/158; Ct=85%, 17/20; p=1.00). Same trends were found in subsets of a) patients’ oocytes (LBR: Et=90%, 85/94; Ct=85%, 11/13: p=0.87), b) donor oocytes (LBR: Et=80%, 52/55; Ct=86%, 6/7; p=1.00), and c) patients grouped by age, both in young women (LBR: Et=85%, 78/92; Ct=80%, 8/10; p=1.00) and older women (LBR: Et=88%, 60/68; Ct=92%, 12/13; p=1.00).
Conclusion: The probability of achieving a clinical pregnancy is higher following the transfer of an expanded blastocyst. However, once a clinical pregnancy is established, the likelihood of live birth or miscarriage remains similar.