Progesterone Luteal Support in Unexplained Infertility Management

The purpose of this study is to evaluate whether progesterone in women with unexplained infertility can increases live birth rate. The main research question is: Does luteal phase support with progesterone increase the live birth rate among couples with unexplained infertility? The study compares progesterone with placebo to determine the effectiveness of progesterone in unexplained infertility. Study participants will: * Perform home ovulation tests and maintain a digital diary to record menstrual cycles and study medication use.10 * Take progesterone or placebo twice daily during the luteal phase of each menstrual cycle for up to six months.11 * Continue usual medical care. No additional hospital visits or invasive procedures are required as part of the study.

Inclusion Criteria: * Primary or secondary infertility for at least a period of 1 year Participants whose previous pregnancy was achieved through MOH-IUI or IVF are eligible to join the study, provided they are willing to continue expectant management for at least six months before considering any further fertility interventions * Diagnosis of UI after infertility work-up, i.e. * regular menstrual cycle ranging between 21-35 days, * total motile sperm count ≥ 10 million/ml, * no risk of tubal pathology (or in case of increased risk, tubal pathology uitgesloten middels tubal patency testing) * A Hunault prognostic score ≥ 30% (calculated using the Hunault prediction model7, based on key prognostic factors including female age, subfertility duration, type of subfertility (primary or secondary), sperm motility and referral status), * Assignment to expectant management during at least six months, in accordance with Dutch NVOG Guidelines (4). * Female age ≥18 years old Female * BMI \