Aim
To evaluate the effects of offering a clinic-driven lifestyle intervention programme in the waiting time before fertility treatment to women and men with obesity (body mass index [BMI] ≥ 30 kg/m2).

Methods
This prospective intervention study was conducted at a public Danish fertility clinic. All consecutive patients, both women and men, referred to the clinic between May 2020 and March 2021 with a BMI ≥ 30 kg/m2 were offered a 6-month lifestyle intervention programme consisting of monthly motivational dialogues and counselling with a certified nutritionist nurse. Weight loss maintenance was evaluated at a 1-year follow-up visit conducted 6-months after completion of the programme. The primary outcomes were absolute weight loss (kg) and relative weight loss (percent compared with weight at inclusion) upon completing the 6-month programme and at the 1-year follow-up. Secondary outcome measures were effects on biochemical metabolic markers.

Results
Forty-five participants were enroled in the study, of which 38 completed the 6-months lifestyle intervention programme and 33 participated in the 1-year follow-up. The participants' mean weight loss was 5.4 kg (95% confidence interval [CI]: 3.3, 7.5) after the 6-month programme (30 of 38 participants lost weight) and 4.4 kg (95% CI: 1.4, 7.3) at the 1-year follow-up compared with baseline. Previously undiagnosed metabolic conditions were revealed in 61% of the participants, including four cases (11%) of undiagnosed diabetes mellitus type 2.

Conclusion
A clinic-driven lifestyle intervention programme offered to patients with obesity in the waiting time for fertility treatment can successfully reduce weight in a high number of patients with stable results at 1-year follow-ups. Metabolic conditions, including diabetes mellitus type 2, are likely underdiagnosed in this group of patients, but further studies are needed.