Couples diagnosed with unexplained subfertility are advised to start mild ovarian hyperstimulation and intrauterine insemination (MOH-IUI) as a primary treatment. Natural feedback mechanisms and hormone release are affected by artificially stimulated cycles and induced ovulation. Additional luteal support could positively affect progesterone patterns in the luteal phase. The LUMO study evaluates whether the addition of exogenous progesterone in the luteal phase following MOH-IUI treatment cycle will improve pregnancy and live birth rates.

A multicentre randomised, double-blind, controlled trial will be conducted in Dutch fertility clinics, academic and non-academic hospitals. There are two treatment arms: group A progesterone luteal phase support; group B placebo, without crossover. All initiated MOH-IUI cycles within 6 months after randomisation are included (study period). Participants will start study medication, applying a daily dosage of 2dd 300 mg progesterone (Utrogestan) or 2dd 300 mg placebo in vaginal capsules on the second day after the IUI procedure. Treatment is continued until the onset of menstruation, a negative pregnancy test (IUI+14 days), a miscarriage or until 7 weeks of gestation in case of a viable pregnancy. Follow-up ends at 12 months after the end of study period (18 months after study randomisation). The primary outcome is cumulative pregnancy rate, achieved within 6 months after randomisation, leading to live birth. A total of 1008 patients (504 patients in each group) will be included.

The study was approved by the Central Committee on Research Involving Human Subjects on 30 January 2023. All participating sites have the approval of the local Board of Directors to participate in the LUMO study. An informed consent form will be signed by all participants. Study results will be presented at (inter)national conferences and published in peer-reviewed journals. It is expected that the results of this trial will be used to draft national guidelines on this issue.

The study is registered in the EU CTIS trial register (2022-501534-33-00), the Dutch trial registry (registration number: LTR 24508), ClinicalTrials.gov (NCT05080569) and the WHO registry (universal trial number: U1111-1280-9461).