Cetrotide is used during IVF to prevent premature ovulation, the release of eggs before they’re ready to be retrieved. It works by blocking the hormone signal that triggers ovulation, giving your fertility team control over exactly when your eggs mature. Without this type of medication, premature hormone surges occur in 12% to 25% of stimulation cycles, which can force a cycle to be cancelled or reduce the number of viable eggs collected.
How Cetrotide Prevents Premature Ovulation
During a normal menstrual cycle, your brain releases a burst of luteinizing hormone (LH) that tells the ovaries to release an egg. In IVF, you need multiple eggs to grow to the right size before retrieval, so that LH surge has to be suppressed until your doctor is ready to trigger it on purpose.
Cetrotide contains cetrorelix acetate, which competes with your body’s natural signaling hormone (GnRH) for the same receptors in the brain. By occupying those receptors, it blocks the message that would otherwise cause an LH surge. This suppression kicks in within about 8 hours of injection and lasts as long as you keep taking the medication daily. Once your follicles have reached the target size, your doctor administers a “trigger shot” to induce the final maturation of eggs, and Cetrotide is stopped.
When You Start and Stop Taking It
Cetrotide enters the picture partway through your stimulation cycle. You’ll begin injectable fertility hormones on cycle day 2 or 3 to encourage multiple follicles to grow. Cetrotide is then added on stimulation day 5 or 6, once the follicles have had a chance to develop but before your body might launch a premature LH surge on its own.
From that point, you take it every day until the trigger shot. The trigger is typically given when ultrasound shows that at least three follicles have reached about 17 mm in diameter. Egg retrieval follows 35 to 36 hours later. So in a typical cycle, you might use Cetrotide for anywhere from 4 to 7 days, depending on how quickly your follicles respond to stimulation.
The Two Dosing Options
There are two FDA-approved regimens. The one used most commonly today is the multiple-dose protocol: a 0.25 mg injection given once daily starting on stimulation day 5 or 6 and continued through the trigger day. This gives your clinic flexibility to adjust timing based on how your follicles are growing.
The alternative is a single-dose protocol: one 3 mg injection given around stimulation day 7, which suppresses LH for about four days. If the trigger shot hasn’t been given within those four days, you switch to daily 0.25 mg doses until it is. This regimen means fewer injections overall but less scheduling flexibility, so most clinics default to the daily low-dose approach.
How to Give the Injection
Cetrotide is a subcutaneous injection, meaning it goes into the fatty tissue just below the skin rather than into a muscle. The recommended site is your lower abdomen, around the belly button. You should rotate to a slightly different spot each day to reduce skin irritation.
The medication comes as a powder in a vial that you mix with sterile water before injecting. The kit includes two needles: a larger one (21-gauge) for mixing the solution and a thinner one (27-gauge) for the actual injection. After dissolving the powder by gently tilting and swirling the vial (not shaking hard, which creates bubbles), you draw the solution into the syringe, swap to the smaller needle, and inject. The whole process takes a few minutes once you’ve done it a couple of times. Your clinic will walk you through it before your first dose.
Store the medication in the refrigerator between 36°F and 46°F (2°C to 8°C), and keep it in the outer carton to protect it from light.
Common Side Effects
The most frequently reported side effects are mild and localized. Redness, itching, swelling, or bruising at the injection site are all common and typically resolve on their own. Headache and nausea also occur in some people.
Less common but more concerning symptoms include severe bloating, pelvic pain, rapid weight gain, decreased urine output, and shortness of breath. These can be signs of ovarian hyperstimulation syndrome (OHSS), a condition related to the overall IVF stimulation process rather than Cetrotide specifically. If you experience those symptoms, contact your clinic promptly.
Cetrotide vs. Ganirelix
Ganirelix is the other widely used GnRH antagonist in IVF, and the two medications work through the same mechanism. A large retrospective study comparing them found no statistically significant difference in outcomes. Clinical pregnancy rates were 54.8% with Cetrotide and 56.2% with ganirelix. Live birth rates were similarly close at 47.2% and 49.4%, respectively. The choice between them usually comes down to clinic preference, insurance coverage, and drug availability rather than any meaningful difference in effectiveness.
Where Cetrotide Fits in the Bigger Picture
Cetrotide belongs to the “antagonist protocol,” one of the two main approaches to preventing premature ovulation during IVF. The older alternative, called an agonist or “long protocol,” uses a different class of medication started weeks before stimulation to shut down your hormonal signals entirely before building them back up with injectable hormones. The antagonist protocol with Cetrotide is shorter, requires fewer total injection days, and carries a lower risk of ovarian hyperstimulation, which is why it has become the more common choice at most fertility clinics.
Cetrotide doesn’t affect egg quality or fertilization rates on its own. Its job is simply to hold off ovulation long enough for the rest of the IVF process to work as planned. The stimulation medications do the heavy lifting of growing follicles, and the trigger shot handles the final maturation step. Cetrotide is the guardrail that keeps the timeline under your clinic’s control.