PurposeTo explore the efficacy and safety of individualized follitropin delta dosing, based on serum anti-Müllerian hormone (AMH) concentration and bodyweight, in a long gonadotropin-releasing hormone (GnRH) agonist protocol.MethodsClinical outcomes after one treatment cycle are reported in women with AMH: 5–35 pmol/L. Oocytes were inseminated by intracytoplasmic sperm injection, blastocyst transfer was on Day 5 and remaining blastocysts were cryopreserved. Data collection included live births and neonatal health follow-up for all fresh/frozen transfers performed within one year after treatment allocation.ResultsIn total, 104 women started stimulation, of whom 101 had oocyte recovery and 92 had blastocyst transfer. The average daily dose of follitropin delta was 11.0 ± 1.6 µg and the duration of stimulation was 10.3 ± 1.6 days. The mean number of oocytes was 12.5 ± 6.4, the mean number of blastocysts was 5.1 ± 3.4, and 85% had at least one good-quality blastocyst. Following mostly single blastocyst transfer (95%), the ongoing pregnancy rate was 43%, the live-birth rate was 43%, and the cumulative live-birth rate was 58% per started stimulation. There were 6 cases of early OHSS (5.8%) graded as mild (n = 3) and moderate (n = 3) and 6 cases of late OHSS (5.8%) graded as moderate (n = 3) and severe (n = 3).ConclusionIn this first evaluation of the individualized follitropin delta dosing in a long GnRH agonist protocol, the cumulative live-birth rate was high. A randomized trial comparing follitropin delta in a long GnRH agonist protocol versus in a GnRH antagonist protocol should provide further insight into the efficacy and safety of this treatment option.Trial registration numberNCT03564509; June 21, 2018.