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A groundbreaking fertility study led by Prof Alex Miras, Professor of Endocrinology at the Ulster University School of Medicine has found that women experiencing fertility challenges who are treated with bariatric surgery have significantly enhanced chances of becoming pregnant than those offered non-surgical medical interventions.

Focusing specifically on the hormonal condition polycystic ovary syndrome (PCOS), the BAMBINI trial represents an international breakthrough in fertility research as the first medical study to compare the treatment method of bariatric surgery with medical interventions for obesity, such as behavioural modification and weight loss medication, in women experiencing fertility challenges.

The most common hormonal disorder in women of reproductive age, women living with PCOS have a 15 times higher risk of not being able to conceive due to low ovulation levels, and a 2-3 times higher risk of adverse pregnancy outcomes than women without PCOS.

Specifically, the BAMBINI trial considered the large unmet clinical need for the management of obesity in women with PCOS, a condition that has a major negative effect on physical health and quality of life.

Previous observational studies have indicated that bariatric surgery could improve ovulation rates and prospects of fertility, however the BAMBINI trial is the first international study to compare the efficacy of bariatric surgery with medical treatments for obesity in a gold-standard randomised, multi-centre study.

From a limiting diagnosis to ‘life-changing’ treatment

Charlotte, aged 29 from London, was one of the 80 women who participated in the randomised trial, which was carried out from 2019 to 2023. Diagnosed with PCOS some years ago, Charlotte was told she would find it difficult to conceive due to irregular ovulation cycles.

After some apprehension, Charlotte underwent bariatric surgery as part of the trial in July 2021 and, in late 2023, welcomed her first daughter. Charlotte said: 

“When I was diagnosed with PCOS, I was told I would find it very difficult to conceive. That was a scary thought at the time and my cycles were so irregular I thought it wouldn’t change. After receiving a letter about the trial, I was very reluctant to have surgery, but was randomly selected to be in surgical group and the team supported me as I made that important decision. I went ahead with the surgery in July 2021, and it has absolutely changed my life. I have lost 85 lbs, my cycles are now every 28 days, and I have since welcomed my baby girl who is alert and clever and doing so well. The trial has changed my eating habits, I now process hunger a lot differently, and the follow up appointments with the dietician have been really helpful. From a low point when I was diagnosed to welcoming my daughter last year, taking part in this trial has changed my life for the better.”


Examining 80 women over the age of 18 who live with PCOS, participants were split into two groups, the first of which received medical treatments for obesity in the form of sessions with a dietician and prescribed medication often used for the treatment of PCOS (metformin and Orlistat). The second group underwent bariatric surgery (sleeve gastrectomy) with a standard multidisciplinary team follow-up in London and Coventry. Over the year that followed, the surgical group was found to have a significantly higher rate of spontaneous ovulation, approximately 2.5 times greater than that of the medical group. This means that those who underwent bariatric surgery began producing eggs naturally following their treatment.

On completion of the comparative study, it was concluded that bariatric surgery was more effective than medical care for the induction of spontaneous ovulation in women with PCOS and could therefore enhance their prospects for fertility.

Completed in 2020 and 2021, the study also found that the women in the surgical group had healthier markers of heart or metabolic disease in the year that followed their surgery than the medical group, which could translate to less complicated pregnancies and reductions in the development of type 2 diabetes and cardiovascular disease later in life, however further research will be required to confirm this theory.

The study titled Bariatric Surgery for Spontaneous Ovulation in women living with Polycystic Ovary Syndrome in the UK: the BAMBINI multicentre, open-label, randomised controlled trial was published in The Lancet medical journal.

Professor Alexander Miras, Clinical Professor of Medicine at the Ulster University School of Medicine, said:

“We are pleased to bring the BAMBINI trial regarding women living with polycystic ovary syndrome to publication. As the first trial of its kind to compare bariatric surgery with medical treatments for obesity, and the first to examine its safety as an option, the results will help women with PCOS and healthcare professionals make better informed decisions about treatment. The treatment of obesity in this group of women is not cosmetic; it could have a life-changing impact. The same applies to many other complications of the disease of obesity. As we present our findings, we hope the results will impact outcomes in future and provide hope to women with PCOS and obesity who hope to one day have children.”

Tim Brundle, Director of Research and Impact at Ulster University, said:

“At Ulster University, we are proud of the role our researchers play in transforming lives and ultimately improving people’s health. We are pleased to see the work led by Professor Alex Miras to identify the link between bariatric surgery and improved fertility outcomes in women living with PCOS published in one of the most prestigious scientific journals. This breakthrough in fertility research is one that we hope will change the outcomes for many women who have experienced challenges when trying to conceive, or who are struggling with the effects of PCOS on their life.”