Co-investigators have left and not been replaced.

Patients will be randomly assigned to a group where they undergo a 12-week lifestyle modification program prior to their fertility treatment, or a group where they are entitled to start their fertility treatment without prior lifestyle modification program.

When allocated to the control arm patients will receive the standard of care combined with the foreseen questionnaires and bio-electric impedance analysis for body composition and ergospirometry. When the patient is allocated to the interventional arm she will receive a 12-week lifestyle modification program prior to her fertility treatment. The lifestyle modification program will consist of dietary advice, advice for physical activity and emotional support. After the 12-week program the fertilty treatment will start as per routine practice. Questionnaires, ergospirometry and bio-electric impedance analysis will also be performed at the foreseen moments.

Inclusion Criteria:

• Subfertile patients between >18- <38 years old requesting fertility treatment at our centre
• PCOS phenotypes A, B, C and D according to the NIH 2012 extension of the ESHRE/ASRM 2003 diagnostic criteria
• BMI >27 and <38 (Jiskoot et al. 2017)
• Nulliparous women
• Patient gives consent voluntarily

Exclusion Criteria:

Patients will be excluded if they:

• do not meet the ESHRE/ASRM 2003 diagnostic PCOS criteria
• Have a BMI <27 and >38 (Jiskoot et al. 2017)
• Need Surgical sperm retrieval
• Use donor eggs
• Need Pre-implantation genetic testing (PGT)
• Multiparous women
• cannot reliably fill out the questionnaires or comprehend the intervention, because of a language barrier