OHSS: ovarian hyperstimulation and how it is prevented today

During ovarian stimulation, the medication encourages several follicles to grow at once. In some women the ovaries react more strongly than expected, and after the maturation trigger substances are released that make fluid pass from the blood vessels into the abdomen. This causes bloating, discomfort and, in severe forms, a large fluid build-up, thickening of the blood and problems with the kidneys and breathing.

It is important to distinguish the forms. Mild bloating and discomfort after egg retrieval are common and settle on their own. Moderate OHSS needs closer follow-up. Severe OHSS, once a feared complication of IVF, needs hospital treatment, but is seen far less often today than two decades ago, precisely because of changes in how stimulation is done.

The risk of OHSS is linked to how strongly the ovaries respond. It is higher in women with PCOS, those with a high AMH or many antral follicles, young and slim women, and those who have had OHSS before. During the cycle, a very large number of follicles on ultrasound and very high oestrogen levels are signs the team follows closely.

Risk assessment begins before the cycle, with AMH and the antral follicle count, and continues during stimulation. This allows the protocol and dose to be chosen carefully from the start, and the plan to be changed along the way if the response turns out stronger than expected. For a patient with PCOS, the conversation about OHSS should be part of planning, not a surprise.

Several changes have made severe OHSS rare. The first is the choice of protocol: antagonist protocols and progestin-primed protocols (PPOS), where oral progesterone is used to prevent premature ovulation, allow better control and open the way to the second step. The second is triggering egg maturation with a GnRH agonist instead of classic hCG in high-risk patients; this markedly lowers the risk because its effect is short.

The third, and often decisive, is the strategy of freezing all embryos, 'freeze-all', with transfer in a later cycle. Because pregnancy in the same cycle worsens OHSS, avoiding a fresh transfer at high risk removes that worsening. Together these measures have transformed OHSS from a major fear into a manageable risk, and they are the area where research, including Dr. Göksu's, continues to refine protocols.

After egg retrieval it is normal to feel a little bloated and to have mild discomfort for a few days. Drink fluids, avoid heavy activity and follow the team's instructions. In most cases everything settles within a week.

There are some signs that call for an immediate phone call, day or night: rapid swelling of the abdomen, rapid weight gain over a few days, severe abdominal pain, vomiting that does not stop, difficulty breathing, and very little urine. These should not wait until morning; the team will assess with ultrasound and tests and decide whether closer follow-up or treatment is needed.