Causes & Treatment

OHSS – Ovarian Hyperstimulation Syndrome Prevention Tips and UK Figures

Eloise Edington  |   13 Feb 2021


What Is OHSS?

One in eight IVF cycles results in the potentially serious side effect, OHSS, or Ovarian Hyperstimulation Syndrome. It is therefore wise to be forewarned and if you have PCOS, you need to be especially careful. However, it is reassuring to know that competent fertility clinics will take steps to minimise the risks of OHSS. Read on to discover about the reporting of the latest figures on incidence of OHSS, as well as some advice on how to help prevent it

OHSS Incidents Drop by a Quarter Due to New Reporting Methods

Words by Sophie Braybrook

The number of Ovarian Hyperstimulation Syndrome (OHSS) incidents reported have decreased by a quarter in 2019/20, compared to the previous year, according to latest figures. OHSS is a potentially serious side effect of the hormones women take during IVF treatment; it occurs when the ovaries swell with fluid which then leaks into the body. Symptoms include severe abdominal pain, development of blood clots and difficulty breathing. The latest 2019/20 figures show the lowest OHSS incidents on record, following the previous year which saw record-high numbers.


The significant reduction in incidents seems to be a result of the way fertility clinics report cases of OHSS, rather than any actual reduction in the number of OHSS incidents. In 2019, the Human Fertilisation and Embryology Authority (HFEA), the non-departmental public body of the Department of Health and Social Care which collects UK fertility data, changed the rules around how fertility clinics should report OHSS. Rather than reporting all cases of OHSS, the HFEA now asks clinics to only report severe cases, ignoring mild and moderate incidents.

Eleanor Gallegos, a reproductive science practitioner at London’s IVI fertility clinic, explained that the significant statistical reduction is “Due to the change in reporting, nothing has changed in terms of stimulation,” Gallegos confirmed, “we still use the same levels of hormones as before…” When I approached the HFEA to comment on why they no longer require clinics to report mild and moderate cases of OHSS, a spokesperson responded with the following:

“OHSS is a serious condition and we want to reduce it as much as possible. It is mandatory for all UK clinics to report details of all severe and critical cases of OHSS… so we are confident that we have a good picture of the most serious cases.”

The HFEA did acknowledge that “Mild or moderate cases, which are less serious but still very worrying for patients, may also involve a hospital admission and are therefore included in the NHS data.”

The HFEA’s acknowledgement of the severity of mild or moderate cases, which often involve hospitalisation and are therefore reported by the NHS, has only increased my concerns regarding their recent exclusion from HFEA data collection. An analysis of their data reveals that the impressive-looking reduction in case numbers is directly related to reporting changes rather than any real industry achievement.

Related Article – Five Essential Functional Medicine Tests for Fertility


Preventing the Risk of OHSS

Most fertility clinics take the prevention of this condition very seriously and seek to minimise / prevent the risks of OHSS in a variety of ways.  When making your choice of fertility clinic, it is a good idea to talk about OHSS and to ask how they manage it. If you don’t feel you are getting a reassuring answer, then look for another fertility clinic.

Have the right pre-assessment fertility tests close to your treatment

Don’t rely on the results of old fertility tests. Have the right pre-treatment assessment prior to beginning the IVF round.  It is essential to have a trans-vaginal scan before treatment, from which your fertility clinic will be able to tell if you are multi-follicular (a red flag for OHSS). Ensure you have a blood hormone profile, to ascertain the ratio between FSH and LH scores, as this can indicate PCOS.  If you have an unusually raised AMH score, this can also be a predictor.

Regular scans at your fertility clinic / watching your stimulation

When you’re in the stimulation phase, ensure you’re having regular scans. The fertility specialist should be checking the follicles are the correct size(s) and watching the number closely. Your fertility clinic/ specialist should also be carefully monitoring your drug/stimulation dosage, to ensure this isn’t too high, keeping you on the appropriate dose of gonatrophins. Having stimulation at the minimal level lowers the risk of OHSS.

IVF trigger shot and egg retrieval

Another precaution against OHSS is the choice of med for the trigger shot. Women who either have PCOS or are susceptible to OHSS may be prescribed a different trigger shot. This is a question to ask your fertility clinic. It may also be that your specialist will recommend delaying egg retrieval, either if your growing follicles are not reaching optimal size, or if you are developing too many follicles.

Postponement of transfer

If there is a risk of OHSS, after retrieval and fertilisation of your eggs, many clinics will prudently recommend freezing the embryos and delaying transfer.  This will mean coming back for a FET (frozen embryo transfer) after approximately six to eight weeks.  There is no need to be concerned about this as nowadays FETs have as good a success rate as transfer of fresh embryos.

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