OHSS happens when ovaries become inflamed, sometimes because they’re stimulated with medications.
To some degree, ovaries are always inflamed a little bit. But in some people, the inflammatory fluid becomes excessive. The fluid collects in the abdomen, making it very uncomfortable to breathe.
Worse, that fluid shouldn’t be there. The end result is a real risk for blood clots. So clearly, we want to avoid hyperstimulation.
When running an IVF cycle, we hope to obtain twelve to twenty eggs. For the vast majority of people, when retrieving this many eggs, everything will be fine. But OHSS does occur from time to time. The risk is higher when more than twenty eggs are being retrieved.
It’s important for you to know that hyperstimulation is very rare except in the context of IVF. Yes, there are always exceptions, and all fertility doctors can remember an unusual case with far fewer eggs leading to hyperstimulation. But these are the 1 in 500 cases and we’re very alert to the signs of hyperstimulation.
So, what are the risk factors?
Young women are more at risk. We suspect this is because of the greater blood flow that younger people have, leading to increased inflammatory potential. Women under the age of thirty-five are more at risk for hyperstimulation.
2. Being thin
When ovaries swell, there can be a “compartment syndrome”. This means there is simply not enough room in the pelvis.
In larger women, a compartment syndrome is less of a worry, but if you are particularly thin, or notably thin with a firm stomach that will not distend particularly easily, then you will be at increased risk for hyperstimulation symptoms.
3. A high ovarian reserve
This is the number one risk: A high number of resting eggs, all of which can be responsive to the fertility medications.
The best way to quantify your ovarian reserve is with two tests: an ultrasound for taking an “antral follicle count”, and a serum AMH level. Women with an antral follicle count over 40 or with an AMH greater than 30 pmol/L are at risk for hyperstimulation.
I worry most about hyperstimulation for women with a high AMH, under thirty-five, who are thin.
So, what do we do?
We try the stimulation and monitor closely. We encourage a diet that has a lot of sodium: up to 1,200 mg a day on top of the usual recommended amount.
Most importantly, we encourage the individual to look very seriously at a freeze-all approach. That means at retrieval, we freeze all the embryos instead of transferring a few days later.