What Happens to Your Eggs During IVF Stimulation — And Why It's Not Just About Getting More

The Part of IVF Nobody Fully Explains

When most people think about IVF, they picture injections, scans, and egg retrieval. But one of the most misunderstood phases of the entire process is what happens during ovarian stimulation — the 10 to 14 days when your body is guided to grow multiple follicles at once.

Patients are often told to hope for a high egg count, and while numbers do matter, experienced fertility specialists know that stimulation is a careful balancing act. Getting it right can make a significant difference to the quality of eggs retrieved, the embryos that develop, and ultimately, your chances of a successful pregnancy.

At Iswarya Fertility, we find that patients who understand what's happening inside their bodies during this phase feel far less anxious — and are better prepared for the conversations their doctor will have with them along the way.

What Ovarian Stimulation Actually Does

Normally, your body selects just one dominant follicle per menstrual cycle, and that one follicle releases one egg at ovulation. IVF works by temporarily overriding this single-selection process using hormonal injections — typically a combination of FSH (follicle-stimulating hormone) and LH (luteinising hormone).

These medications encourage multiple follicles to grow simultaneously. Each follicle contains one egg, so the goal is to recruit as many mature eggs as possible from a single cycle — eggs that would otherwise be lost that month.

But here's what many patients don't realise: not every follicle that grows will contain a mature, usable egg. And not every egg retrieved will fertilise. And not every fertilised egg will develop into a viable embryo. Understanding this natural attrition helps set realistic expectations from the very beginning.

What Your Doctor Is Watching During Monitoring Scans

Once stimulation begins, you'll attend a series of monitoring appointments — typically every 2 to 3 days. These aren't just routine check-ins. Your medical team is tracking several critical factors:

• Follicle count and size: Follicles need to reach approximately 18–20mm in diameter to be considered mature and ready for retrieval.
• Follicle growth rate: Follicles that grow too quickly or too slowly may produce eggs of poorer quality. The aim is steady, consistent growth.
• Oestradiol levels: This hormone, produced by the growing follicles, gives doctors a window into how the follicles are functioning — not just how large they appear on a scan.
• Endometrial thickness: Although the egg retrieval comes first, your team is already keeping an eye on the uterine lining, especially if a fresh transfer is being planned.
• Signs of ovarian hyperstimulation: If the ovaries are responding too strongly, your doctor may adjust your medication dose or recommend a freeze-all strategy to protect your safety.

This level of monitoring is why IVF requires multiple appointments during stimulation. It is not about being overcautious — it is about tailoring the protocol specifically to how your ovaries are responding, in real time.

Why Egg Quality Matters as Much as Egg Number

It is tempting to focus on how many eggs are retrieved. A higher number feels reassuring. But experienced clinicians always look beyond the count.

Egg quality is primarily determined by two things: your age and how the stimulation protocol was tailored to your body. A woman in her mid-30s who produces 8 good-quality eggs will often have better outcomes than someone who produces 20 eggs with a high proportion of immature or abnormal ones.

Factors that can affect egg quality during stimulation include:

• The stimulation dose — too high a dose can push follicles to grow faster than is ideal
• The length of stimulation — extending it unnecessarily in search of more follicles can compromise egg maturity
• The timing of the trigger injection — this is one of the most precise steps in the entire cycle, as it initiates the final maturation of the eggs before retrieval
• Your ovarian reserve — which reflects the natural pool of eggs available

This is why personalised protocols matter so much. A stimulation plan designed for one patient may be entirely wrong for another, even if their test results look similar on paper.

The Trigger Injection: A Moment That Matters More Than Most Patients Realise

Approximately 36 hours before egg retrieval, you will be given a trigger injection. This step mimics the natural LH surge that causes ovulation — but timed very precisely so that the eggs reach final maturity just before retrieval, without actually ovulating on their own.

There are two main types of trigger injections used in IVF:

1. hCG (human chorionic gonadotropin) trigger: The more traditional option, effective for most patients but associated with a higher risk of ovarian hyperstimulation syndrome (OHSS) in high responders.
2. GnRH agonist trigger: Often used for patients at higher risk of OHSS. It produces a shorter, more natural-looking LH surge and is associated with a lower hyperstimulation risk — though it may require a freeze-all approach rather than a fresh transfer.

Your fertility specialist will determine which trigger is most appropriate based on your response to stimulation and your individual risk profile. Getting this step right is crucial — even the timing down to the hour is important.

What to Expect in the Days After Stimulation

After the trigger injection, most patients feel a sense of fullness or bloating as their ovaries, now enlarged with multiple follicles, prepare for retrieval. This is normal. You may also feel emotional — a combination of hormonal changes, anticipation, and the cumulative stress of the treatment cycle.

Egg retrieval itself is a minor surgical procedure, usually completed in under 30 minutes under light sedation. Most patients return home the same day and resume light activities within 24 to 48 hours.

Within hours of retrieval, your embryologist will assess which eggs are mature, attempt fertilisation using either conventional IVF or ICSI, and begin monitoring embryo development. The stimulation phase may be behind you — but the journey is just beginning.

Ready to Understand Your Own IVF Journey More Deeply?

Every IVF cycle is unique because every patient is unique. The stimulation phase is not a one-size-fits-all process — it requires expertise, careful monitoring, and a willingness to adapt the protocol as your body responds.

At Iswarya Fertility, our specialists take time to explain each step of your treatment, so you understand not just what is happening, but why. If you have questions about IVF stimulation, your ovarian reserve, or how to get started, we invite you to book a consultation with our team. Knowledge is one of the most powerful tools you have on this journey — and we're here to give it to you.