Presentation (CTI)

OBJECTIVES: Background: In IVF-treatment, elective freezing of all embryos (“freeze-all”) has been suggested as an alternative to fresh embryo transfer following ovarian stimulation to mitigate potential adverse effects on hormone levels, which might compromise endometrial receptivity and reduce implantation. The “freeze-all” strategy is not routinely applied in Denmark as evidence from randomized controlled trials has not demonstrated higher birth rates compared with fresh embryo transfer. However, evidence from real-world clinical practice remains limited.
Aim: To compare pregnancy outcomes following elective freeze-all versus fresh embryo transfer in IVF-treatment.
METHODS: Methods: This nationwide cohort study used data from the Danish IVF-Register and National Prescription Register. The study population comprised 20,312 women undergoing a total of 36,035 IVF treatments with ovarian stimulation medication and an embryo transfer between January 2021 and September 2025. The outcome was clinical pregnancy confirmed by ultrasound at gestational week 7. Pregnancy rates were compared between fresh and frozen embryo transfers at the first transfer attempt following oocyte aspiration. Multivariable regression models were used to estimate odds ratios (ORs), adjusting for year, age, BMI, cause of infertility, public/private clinic, stimulation cycle number, medication product and defined daily doses.
RESULTS: Results: The proportion of IVF-treatments with frozen embryo transfers increased from 6% in 2021 to 38% in 2025. Pregnancy was obtained in 40% (3,614/8,987) of frozen embryo transfers compared with 30% (8,232/27,048) of fresh embryo transfer. Frozen embryo transfer was associated with higher odds of pregnancy compared with fresh embryo transfer in both crude (OR 1.54, 95% CI 1.46;1.62) and adjusted analyses (OR 1.26, 95% CI 1.18;1.34).
CONCLUSIONS: Conclusion: In a real-world setting, clinical practice has to a high extent adapted to the freeze-all approach over recent years despite the absence of recommendations. These preliminary findings suggest that a freeze-all strategy may confer a modest improvement in pregnancy outcomes compared with fresh embryo transfer.