Effectiveness and safety of follitropin delta in routine clinical practice in the Nordics and Switzerland (the NORSOS study): a prospective non-interventional study.

Background: Follitropin delta is the first approved human recombinant follicle-stimulating hormone treatment administered through an algorithmic individualized dosing regimen based on body weight and anti-Müllerian hormone (AMH) levels. This study assesses the effectiveness and safety profile of follitropin delta in women naïve to Study design: This prospective observational study was conducted from August 2022 to March 2024 across 14 fertility clinics in Denmark, Norway, Sweden, and Switzerland. Consenting women with infertility (≥18 years old) receiving their first assisted reproductive technology cycle and first follitropin delta treatment were enrolled. Both fresh and frozen embryo transfers were evaluated. Follow-up continued until confirmed pregnancy outcome, early pregnancy loss, or study withdrawal. Data on follitropin delta usage, ovarian stimulation, embryo development, and safety were collected through electronic case-report forms. Patient-reported satisfaction with the follitropin delta pre-filled pen was assessed using patient questionnaires. Results: Of the 201 women enrolled, 199 completed the study. Of these, 147 (73.9%) were aged <35 years (median 32 years). The primary reason for infertility was male factor (88/199, 44.2%). Baseline characteristics included a mean body weight of 68.9 kg, and a mean AMH baseline concentration of 21.3 pmol/L, with 130/199 (65.3%) participants having AMH concentrations >15 pmol/L. Overall, 169/199 (84.9%) participants were prescribed follitropin delta according to the calculated algorithmic dose, with a mean starting dose of 10.2 µg and a mean duration of ovarian stimulation of 9.9 days. The gonadotropin-releasing hormone antagonist protocol was used in 171/193 (88.6%) women. Almost half of the analysis population (93/194, 47.9%) achieved the algorithm-targeted response of 8-14 oocytes retrieved, and >15 oocytes were obtained in 55/194 (28.4%) women. Ongoing pregnancy rate assessed by ultrasonography 10-11 weeks after embryo transfer was 82/155 (52.9%). Ovarian hyperstimulation syndrome (all mild cases) was reported in 8/199 (4.0%) women. Almost all women (190/193, 98.4%) expressed satisfaction with the injection pen. Conclusions: The NORSOS study (NCT05499052) provides insights into the use of follitropin delta in routine clinical practice and complements previous evidence regarding its effectiveness and safety profile.