Q & A with Isaac Evbuomwan, a fertility gynaecologist and Director of Gateshead Fertility, who is an expert in OHSS
What is Ovarian Hyperstimulation Syndrome, or OHSS?
It’s a well known but relatively uncommon complication of fertility treatments which involve stimulation of the ovaries with hormones. It’s most often seen in IVF and ICSI where we stimulate the ovaries with gonadotrophin to help them to produce more eggs, and more embryos. It can occur at different stages. Early onset OHSS happens earlier in the cycle, within seven days of having the IVF trigger shot (hCG hormone) to mature the eggs. That’s often linked to an exaggerated response to the stimulation. It can also happen later, a week to 10 days after the trigger shot, and that tends to be associated with pregnancy as it is linked to the hormones produced in early pregnancy.
So why does it happen? Why do some people get it and not others?
That’s an interesting question and the answer still eludes us. We know a lot about OHSS but we still don’t know why some people get it and others don’t. What we do know is that a relatively small number of patients going through treatment have a strong response to stimulation and end up having OHSS. You can get a patient who has 30 or 40, or even 50 follicles and they don’t get OHSS, while someone else who has 20 follicles will get it. And that’s the difficulty we have – although we know a lot more about OHSS now, we still can’t say for certain whether someone is going to get it or not. I have some theories I’ve been looking at in my research around changes that happen just before the trigger shot, and although it was looking promising, I haven’t been able to follow up on it.
Given what you’ve just said about not always being able to know who’s going to get it, can you prevent it?
I would say yes. Before the trigger shot, you can prevent OHSS by simply stopping the cycle, cancelling it. If you stimulate the ovaries and it looks as if the patient is at high risk of getting OHSS, you can stop it by not giving the trigger injection.
Do you always have to stop the treatment cycle if someone’s showing signs of being at risk of OHSS?
If we always did that, we’d have to cancel too many cycles to prevent just perhaps one or two cases of OHSS. So, it’s uncommon to cancel the cycle at that point. If you’ve already had egg collection and created the embryos, you can reduce the risk by not doing a transfer and freezing the embryos. Then you can transfer the frozen embryos once things are settled down. If you don’t
put fresh embryos back, there’s not going to be any pregnancy, and that way, you avoid the late onset. However, this will not necessarily prevent early-onset OHSS which is more related to excessive response to hormone stimulation.
So who is most at risk?
We know there is a possibility of OHSS if your so-called egg count or ovarian reserve is very high. What I mean by that is, if you have an AMH (anti-mullerian hormone) or antral follicle count (AFC) test that’s on the high side, that puts you at potential risk of getting the syndrome. Having a history of PCOS (polycystic ovary syndrome) potentially puts you at risk too because you tend to have a huge ovarian reserve. And if you’ve had OHSS in the past, that can be a higher risk too. And if you have more than 15 eggs at egg collection, that can add to your risk. There’s a higher risk for young women and apparently for Black women.
If you have those additional risks, we need to choose the right protocol for your fertility treatment. One such protocol is the antagonist protocol. This protocol can minimise the risk because there is less oestrogen produced during stimulation. It also allows you to give a different/alternative type of trigger shot (agonist trigger instead of hCG hormone) which minimises the risk of OHSS. In this instance, you would need to freeze all suitable embryos created with a view to transfer later in a frozen cycle, once things have settled.
So, as a patient, what are the symptoms? How would you know if you’ve got it?
As a patient, the most common symptoms would be having a bloated or tight swollen tummy. Of course, That’s to be expected to some extent though as the ovaries do increase in size when they are stimulated. It can be associated with pain, the type of pain that you’d need to take some sort of pain relief. You may feel nausea or sickness and experience vomiting, and you may notice you aren’t passing as much urine as usual. You may also feel dehydrated, and experience constipation or diarrhoea. You can also experience dizziness and breathlessness. Also, and we don’t see this very often anymore as people are more aware of OHSS earlier, but you can get swelling of the vulva and lower legs which are a much later symptoms.
So, if you are going through treatment and you start experiencing these symptoms, what should you do?
The best bet is to get in touch with your clinic straight away. If you think you have symptoms, get in touch and the clinic will help you make sense of what you’re experiencing. Sometimes it may just be discomfort relating to the procedure as the ovaries are swollen, but the clinic will be able to talk you through what you’re experiencing and work out if you need to go in for an assessment to see whether or not you have OHSS. Your clinic should have given you a number to call but if they haven’t, call your GP or go to A & E if all else fails.
Are there different levels of severity of OHSS?
Most patients have mild OHSS which is just some discomfort and a swollen tummy where there isn’t any nausea or vomiting. You need to do tests to check the severity but with the moderate or severe OHSS, you would have more symptoms.
What treatments are there available for OHSS?
Most treatments are really about managing the symptoms. OHSS is a self-limiting condition so it will run its course, but managing the symptoms makes all the difference. What is most important is to let patients know OHSS won’t affect their chances of success, and if you do get pregnant, it won’t jeopardise the pregnancy. Sometimes we might need to drain some of the fluid in the tummy (ascites) if the OHSS is more severe which is done through the vagina as a day case. We want to address any dehydration, ideally by getting you to drink more fluids (or through a drip if you cannot drink because of nausea and vomiting). We also give you compression stockings as well as heparin injection in order to reduce the risk of developing blood clots in the legs (DVT) or lungs (PE).
And finally, are there any long-term impacts of having had OHSS?
If patients are picked up early and you get on top of the treatment, usually not but the symptoms can make you feel quite poorly, and it can be very unpleasant. That is why it’s crucial to let patients know what to look out for, what to expect, provide them with contact numbers, including out-of-hours and reassure them. Usually, it would only be if you have really bad complications like blood clots that it could potentially have a longer impact.