Ovarian Hyperstimulation Syndrome (OHSS)
OHSS is a potentially dangerous medical condition that can occur in women who have had gonadotrophin for ovulation treatments or IVF therapies. We do not yet fully understand what causes it but we can take steps to minimise its risk/ impact. A small subset, approximately 1-2% of patients will develop what we classify as severe OHSS and require hospitalisation with close, intense medical supervision.
Women who are at more risk are young and thin or with polycystic ovarian syndrome. These patients often achieve excessive egg numbers, which seems to increase the risk of OHSS developing. OHSS is likely to occur in women who develop in excess of 20 eggs, but has been known to occur with fewer eggs. If we think a woman is at significant risk of developing this condition, we can cancel the cycle prior giving the HCG injection that triggers ovulation. This tends to prevent the development of severe OHSS.
The condition may be worsened by the establishment of a pregnancy. Therefore an option is to collect the eggs, fertilise them and freeze all of the embryos with a view to transferring an embryo in a future FET cycle (once the ovaries have returned to normal). There are other methods that may implemented to reduce the risk of OHSS or the severity of its symptoms.
Women with severe OHSS may have dramatic enlargement of their ovaries and fluid shifts from the blood stream into the abdominal cavity, causing distension and discomfort. Fluid may even enter the cavity around the lungs creating breathing difficulties. A further risk is that the decreasing volume of fluid in the blood vessels increases the viscosity (or thickness) of the blood leading to thrombosis or clotting. Some deaths have been recorded overseas from OHSS but thankfully no deaths have been recorded in our country. Needless to say severe OHSS is a potentially very dangerous medical condition.
The risk of OHSS in an otherwise healthy woman has to be balanced against any desire for pregnancy, and while the mechanisms are in place to minimise the risk, it cannot be absolutely avoided.