The REWAG study ("Real-world Evaluation of Women undergoing Agonist protocol with Follitropin delta") is a non-interventional observational study conducted across several fertility centers in Germany. The goal of this study is to evaluate how well a personalized dosing regimen of a hormone called Follitropin delta works in women undergoing controlled ovarian stimulation (COS) for in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) using a long GnRH agonist protocol.

Follitropin delta is a recombinant follicle-stimulating hormone (rFSH) that allows for individualized dosing based on a woman's weight and a blood marker called anti-Müllerian hormone (AMH). This personalized approach may help to better balance the stimulation of the ovaries, aiming to reduce the risk of overstimulation (OHSS) while still achieving good treatment outcomes.

The study will include approximately 350 women who are undergoing routine IVF/ICSI treatment. No experimental drugs or procedures are involved. All treatment decisions remain the responsibility of the attending physicians and follow standard clinical practice. Data will be collected only from routine visits and medical documentation, with no additional interventions required for participation.

Researchers will analyze outcomes such as the number of eggs retrieved, pregnancy rates, treatment cancellations, and any side effects. The study will also look at whether certain patient characteristics can predict how well the treatment works or whether complications may arise.

Participation is voluntary. All personal data will be pseudonymized and handled according to strict data protection regulations (GDPR). Results will help to improve understanding of how personalized hormone dosing performs in real-life settings and may support more tailored and effective fertility treatments in the future.

Inclusion Criteria:

• Age ≥18 to ≤ 44 years at enrolment
• Planned stimulation in a long luteal GnRH agonist protocol with daily s.c. GnRH-agonist
• Planned use of Fd for ovarian stimulation as per SmPC
• Serum AMH ≥0.3 ng/ml to ≤4.9 ng/ml measured within12 months prior to treatment
• Most recent serum AMH value before start of stimulation not older than 12 months
• Planned IVF or ICSI treatment in a first or second attempt with ejaculated or cryopreserved male germ cells, autologous or heterologous, with or without planned genetic testing of the oocytes or embryos
• Planned triggering of final oocyte maturation with hCG
• Willingness and consent to participate

Exclusion Criteria:

• Serum AMH value not determined in ELECSYS AMH Plus Immunoassay, ACCESS AMH Advanced (Beckham Coulter) or LUMIPULSE G AMH (Fujirebio)
• Most recent serum AMH value before start of stimulation older than 12 months
• Serum AMH within 12 months prior to treatment AMH ≤ 0.3 ng/ml or ≥4.9 ng/ml measured within 12 months prior to treatment
• Pre-treatment with a combined oral contraceptive "pill" consisting of ethinyl estradiol and a synthetic progestogen or a natural estradiol/progesterone
• Anovulatory PCOS syndrome
• Women with a contraindication for prescription of Fd treatment
• Women undergoing ovarian stimulation for fertility preservation

Infertile women undergoing IVF oder ICSI. This study is intended to be conducted in non-vulnerable population. No vulnerable subjects will be enrolled in the study.