Ovarian stimulation is the first active phase of an IVF cycle: usually 8 to 14 days of daily hormone injections, punctuated by short monitoring visits, and finished with a precisely timed “trigger” injection about 36 hours before egg collection. Most women find it more manageable than they feared — but knowing what each day actually involves makes the whole process far less daunting.
Before day one: the baseline scan
Stimulation does not begin the moment you decide to start IVF. First comes a baseline appointment, usually on day 2 or 3 of your period. A transvaginal ultrasound confirms that the ovaries are “quiet” — no large cysts or leftover follicles from the previous cycle — and that the uterine lining is thin, as expected at the start of a cycle. A blood test often accompanies the scan, most commonly measuring oestradiol.
If everything looks as it should, you start injections that evening or the next day, with a dose chosen for your age, ovarian reserve and any previous response. If a cyst or a raised hormone level is found, your doctor may delay the start by a few days or a full cycle. That feels frustrating, but it is sensible: beginning on the wrong footing wastes medication and lowers the chance of a good response.
Days 1–4: starting your injections
The main stimulation drug is follicle-stimulating hormone (FSH), given once a day as a small injection under the skin of the abdomen or thigh. Most modern preparations come as pre-filled pens with short, fine needles; the injection takes seconds, and most patients describe a brief sting rather than real pain. Your nurse will teach you the first one, and almost everyone manages independently from day two.
- Inject at roughly the same time each day, usually in the evening — a consistent window matters more than the exact minute.
- Rotate injection sites to avoid soreness or bruising in one spot.
- Mild bruising, redness or itching at the site is common and harmless.
What is the medication doing? In a natural cycle, a group of small follicles begins each month but only one matures. Stimulation simply supports the whole group that was already recruited that month, so several follicles — each hopefully containing an egg — can grow together. It does not “use up” future eggs. If you would like a fuller explanation of each drug, see our guide to IVF medications explained.
In these first days most women feel essentially normal. Mild bloating, tiredness or mood swings may creep in towards the end of the week, but most people continue working and living normally throughout stimulation.
Days 5–8: monitoring scans and dose adjustments
Around day 5 or 6 you return for the first monitoring visit: a transvaginal scan to count and measure the growing follicles, often with a blood test. Follicles typically grow 1–2 mm per day, and each visit gives your team a snapshot of how your ovaries are responding. Expect two to four monitoring visits in total; each takes only 15–20 minutes.
Based on what the scans and bloods show, your dose may be adjusted up or down — this is routine fine-tuning, not a sign that something is wrong. In the widely used antagonist protocol, a second daily injection (a GnRH antagonist) is added around this point to stop your body ovulating before the eggs can be collected.
One honest point deserves emphasis: the number of follicles you grow reflects your ovarian reserve and your biology, not your effort. Some cycles respond quickly, some slowly, and the calendar shifts accordingly — which is why how long IVF takes is always an estimate rather than a promise. Comparing your follicle count with someone else’s is rarely useful and often upsetting; what matters is the plan your own doctor builds around your response.
Days 9–12: the trigger decision
When the lead follicles reach roughly 17–20 mm, your team decides it is time to trigger. The trigger is a single injection — hCG, a GnRH agonist, or occasionally both — that completes the final maturation of the eggs. It is timed to the hour, because egg collection takes place about 34–36 hours later: trigger too early and eggs may be immature; too late and you risk ovulating before collection.
The choice of trigger drug is individual. In women with many follicles, an agonist trigger substantially reduces the risk of hyperstimulation, and is often paired with freezing all embryos and transferring in a later cycle — an approach explained in our article on fresh versus frozen embryo transfer. After the trigger, you stop all stimulation injections; the next step is egg collection.
OHSS: what to watch for
Ovarian hyperstimulation syndrome (OHSS) is the main medical risk of this phase. Mild symptoms — bloating, a feeling of fullness, mild discomfort — are common and usually settle on their own. Severe OHSS is uncommon: HFEA patient guidance puts severe cases at around 1% of cycles, and modern antagonist protocols, agonist triggers and freeze-all strategies have made it rarer still.
Contact your clinic promptly — do not wait for your next appointment — if you notice rapid weight gain, a swollen or painful abdomen, persistent nausea or vomiting, passing much less urine than usual, or any breathlessness. These symptoms are treatable, and treated early they almost always resolve well.
Practical tips patients actually ask about
Storing your pens
Most stimulation pens are kept in the fridge before first use; many can then stay at room temperature for a limited period once opened — check the leaflet for your specific brand. Never freeze them, and keep them out of direct sunlight and hot cars.
If you miss or delay a dose
A dose taken a few hours late very rarely derails a cycle. Take it as soon as you remember on the same day, and telephone your clinic for advice rather than doubling up the next dose. Honesty helps here: tell your team exactly what happened so they can adjust if needed.
Travelling for treatment
If you are coming from abroad, early monitoring can sometimes be done near home with the final scans and egg collection at the clinic — ask before you book flights. Carry medication in your hand luggage with a cool bag and a clinic letter for security, never in the hold, where temperatures can drop below freezing.
Day-to-day life
Work, walking and gentle exercise are fine. Avoid high-impact sport and heavy lifting in the final days, when enlarged ovaries carry a small risk of twisting (torsion). Bed rest is not required at any point.
On paper, stimulation looks like the most demanding stretch of treatment; in practice, most patients settle into the rhythm within a few days. If you are still weighing up treatment as a whole, our overview of IVF treatment walks through every stage from first consultation to pregnancy test.
Sources: ESHRE, HFEA, WHO and accepted reproductive-medicine guidance. This article is for general education and does not replace a medical consultation. Reviewed by Assist. Prof. Dr. Muzaffer Uçarer (Obstetrics & Gynaecology · IVF and Reproductive Medicine), UCARER Women’s Health, Istanbul.
