John: Hello, I'm John Hilton, editor of the Cochrane Editorial unit. Some women who have ovarian stimulation for assisted reproduction will experience an adverse effect called ovarian hyperstimulation syndrome, or OHSS. There are several Cochrane Reviews of strategies to prevent this and a new overview in January 2017 brings together the findings from these systematic reviews. The lead author, Selma Mourad from Radboud University Medical Centre in Nijmegen in the Netherlands summarises this large evidence base in this podcast.

Selma: Ovarian hyperstimulation syndrome is caused by a very high ovarian response to hormonal medication and results in enlarged ovaries and a fluid shift from blood vessels to the abdominal cavity, leading to abdominal bloating, a high risk of blood clots and decreased blood supply to important organs such as the kidneys and liver. The mild form of OHSS is seen in 20% to 33% of assisted reproductive technology cycles, whereas a moderate or severe form is found in approximately 3% to 8% of cycles.
Our overview of 27 Cochrane reviews summarises the available evidence on interventions that could prevent or treat moderate, severe and overall OHSS in couples with subfertility who are undergoing assisted reproductive technology cycles, such as in vitro fertilisation and intracytoplasmic sperm injection. Seventeen of these 27 reviews had been done, or updated, in the past three years.
In total, seven reviews described interventions that provided a beneficial effect in reducing OHSS rates, and one additional review showed 'promising' results. Of the effective interventions, all except one had no detrimental effect on pregnancy outcomes. The reviews that provided moderate or high quality evidence of benefit indicate that clinicians should consider the following interventions in particular: metformin treatment before and during an ART cycle in women with polycystic ovarian syndrome and gonadotrophin-releasing hormone antagonists in ART cycles or as a trigger in donor oocyte or 'freeze-all' programmes. A promising intervention that needs to be researched further is coasting, the withholding of gonadotrophins for reduction of OHSS. On the other hand, the evidence is currently insufficient to support the widespread practice of freezing all embryos and replacing them at a later time when OHSS has dissolved.
In conclusion, our overview should help policymakers to develop local and regional protocols or guidelines for the prevention of OHSS and we hope it will also encourage future research to fill the knowledge gaps. Clinicians can use the summarised evidence now to help them to choose the best treatment regimen for individual women, which would be one that reduces the chance of developing OHSS but does not compromise pregnancy outcomes. Unfortunately, our conclusions are limited by a lack of recent primary studies and updated reviews, and some of the novel strategies for preventing OHSS that are not yet described in Cochrane reviews, cannot, of course, be included in our overview.”

John: If you would like to read this one stop guide to the more than two dozen Cochrane Reviews that are currently available, you can find the overview online at Cochrane Library dot com, with a simple search for 'overview of OHSS'.