IVF Side Effects: What OHSS Is and How It Is Prevented

Ovarian hyperstimulation syndrome is an exaggerated response to fertility drugs in which the ovaries swell and fluid shifts out of the bloodstream into the abdomen. It is the main serious risk of a stimulation cycle, and it is largely preventable.

Most cases are mild: bloating, discomfort, a sense of fullness. The concern is the moderate and severe end, where fluid accumulation, haemoconcentration and, rarely, clotting complications can require admission.

• Mild — bloating and discomfort, common and self-limiting.
• Moderate — more marked distension, nausea, ultrasound-visible fluid.
• Severe — significant fluid shift, requiring medical management.
• Severity is a spectrum, not three separate conditions.

Severe OHSS after an hCG trigger may occur in 1–2% of a relatively young IVF population, aged 18 to 36, treated on a GnRH-antagonist protocol. That is a real risk and a small one, and both halves of that sentence matter.

The predictors are known before stimulation begins, which is what makes prevention possible. ASRM recommends counseling patients with elevated anti-Müllerian hormone levels, polycystic ovary syndrome, and anticipated high oocyte yields that they are at increased risk.

• High AMH — more follicles available to respond.
• PCOS — characteristically high antral follicle counts.
• A high anticipated oocyte yield in this cycle.
• Previous OHSS in an earlier cycle.

This is one of the clearest uses of ovarian reserve testing. Predicting how a cycle will respond is the job those markers were designed for, unlike predicting whether you will conceive — a distinction covered in our article on AMH.

Being high risk does not mean a cycle cannot go ahead. It means the protocol should be built differently from the start.

• What Is Ovarian Hyperstimulation Syndrome (OHSS)?
• What Is Diminished Ovarian Reserve? What the Tests Do and Do Not Tell You (2026)
• Endometriosis and IVF: What the Evidence Says About Surgery First
• After a Failed IVF Cycle: What Is Worth Investigating
• Implantation Symptoms After IVF: What’s Normal and What’s Not
• PGT-A in IVF: What the Evidence Shows About Testing Embryos
• Fertility Tests for Women: What Each One Checks, and When

By protocol choice, dose and trigger, in that order. ASRM makes a strong recommendation, supported by strong evidence, to use GnRH antagonist protocols rather than agonist protocols where there is concern about OHSS.

Dose matters next. Choosing the FSH dose according to ovarian reserve testing rather than a standard starting dose is associated with a lower incidence of moderate or severe OHSS — fewer follicles recruited in the first place.

• Antagonist protocol where OHSS is a concern — strong recommendation.
• FSH dose based on ovarian reserve testing, not a default.
• Cabergoline from the day of hCG trigger in at-risk patients.
• Freeze-all, deferring transfer, avoids the pregnancy-driven second phase.

For patients at risk of moderate to severe OHSS, ASRM recommends starting a dopamine agonist such as cabergoline on the day of the hCG trigger or soon afterwards, continued for several days.

Our comparison of antagonist and agonist protocols covers what the wider trial evidence shows about the two approaches.

Escalating rather than static symptoms, and anything affecting breathing or urine output. Mild bloating after retrieval is expected; a rapid change is not.

• Rapid weight gain or quickly increasing abdominal swelling.
• Severe abdominal pain, persistent vomiting.
• Shortness of breath or difficulty lying flat.
• Passing much less urine than usual.

Clinics expect these calls and would rather take one that turns out to be nothing. Waiting to see whether it settles is the wrong instinct with OHSS, because the fluid shift can progress over hours.

The other side of this is that most people having a cycle will feel bloated and uncomfortable for a few days and will be entirely fine. Knowing which symptoms matter is more useful than watching for all of them.

Timing helps too. Early OHSS appears within about a week of the trigger and reflects the drugs; late OHSS appears later and is driven by a pregnancy producing hCG of its own. That is the reasoning behind a freeze-all strategy in high-risk cycles — deferring transfer removes the second driver entirely.

Side effects of fertility drugs attract a lot of claims, and the ones that circulate most are not the ones with evidence behind them.

• OHSS is not an inevitable part of IVF; it is largely preventable.
• No supplement or diet has been shown to prevent OHSS.
• Drinking large volumes of water does not treat established OHSS.
• A canceled or converted cycle is a safety decision, not a failure.

If your protocol is not being adjusted despite high AMH or PCOS, that is a reasonable question to raise before starting rather than after. A clinic that has already planned for your risk will be able to say what it changed and why.

Comparing centres locally helps: our directory covers fertility clinics in Basavanagudi, each with an IVY Score built from the same five signals, alongside the other 37 areas of the city.