Ovarian hyperstimulation syndrome (OHSS)

What is OHSS?

OHSS occurs when your ovaries over-respond to FSH injections. FSH injections stimulate your ovaries to produce many egg sacs (follicles). When a large number of follicles are produced it is possible that your ovaries will enlarge and release chemicals into your bloodstream that make blood vessels leak fluid into the body.

OHSS is classified as mild, moderate or severe.

What are the symptoms of OHSS?

• Mild OHSS - abdominal swelling, feeling bloated, nausea, heartburn or indigestion
• Moderate OHSS - the symptoms of mild OHSS increase as fluid may be building up in the abdomen. There is increased abdominal pain and vomiting
• Severe OHSS - the most severe form of OHSS only occurs in 1 – 1.5% of patients. It is characterised by nausea, vomiting, ovarian enlargement and ascites, causing marked abdominal pain and distention. The abdominal distention may prevent the proper movement of the diaphragm (the muscle between the chest and abdomen) so that you feel extremely breathless. You may feel weak and faint due to a reduction in circulating blood volume (hypovolaemia). In the most extreme situations there is a reduction in the blood flow through the kidneys, resulting in a reduction in urine output. If this occurs it may lead to renal failure requiring treatment with renal dialysis.
  

If you develop severe OHSS you will need hospital admission, usually for a few days, occasionally for longer, to relieve you symptoms and monitor your progress. If you are admitted to hospital give your OHSS card to nursing staff immediately.

Management of severe OHSS may include aspiration of some ascitic fluid from your abdominal cavity. It will include maintaining the circulating blood volume by administering intravenous fluids, which will also substitute the fluids lost by vomiting.

Impact of OHSS on treatment

If there are signs of moderate to severe OHSS prior to the egg collection we may advise you not to have the trigger injection of Human Chorionic Gonadotrophin (hCG) to mature the eggs. Note: you must not have unprotected intercourse (use a condom) at this stage. Your egg collection will be cancelled and you must continue on the down- regulation drugs until all the follicles have collapsed. Once this has happened, a new cycle of treatment with a lower dose of FSH injections can be restarted.

If at egg collection a large number of eggs are harvested we may advise that all suitable embryos are frozen and stored, to be transferred at a later date. This is because the hormone produced when a pregnancy occurs will exacerbate any OHSS already present. Therefore it would be unwise to transfer an embryo until all of the follicles have collapsed and the hormone levels returned to normal. The stored embryos would then be thawed and transferred at a later date.

Some patients could still develop OHSS in the two weeks after their egg collection. The majority will develop a minor or moderate form of the condition - their ovaries become enlarged with multiple cysts and ascites (fluid in the abdominal cavity), causing abdominal discomfort.

OHSS symptoms can be exacerbated by pregnancy but usually do not persist after the first three months when the hormone production supporting the pregnancy shifts from the ovaries to the placenta. In the majority of cases the symptoms disappear within a few weeks. Those patients who are not pregnant recover much more quickly, usually by the time they have their next period.