Zaza,
Thanks. When you start ivf, you'll get a photocopy of some notes and Dr Yong will explain to you about the risks of hyperstimulation.
From what I understand, the water is leaked to the addomen area instead of going into the bloodstream. This means that the blood becomes thicker and the person may be in risk of blood clots, which can be fatal.
The other problem is if there is too much water, it may go up to the lungs and caused breathing difficulties. In more severe cases, OHSS patients need to be warded so that water can be drained off their bodies.
From what I read, most of the OHSS patients has > 20 follicles and high E2 reading.
Hope this information helps you in your journey of ivf. All the best!