Most people find the injections cause mild stinging or bruising rather than significant pain. Egg retrieval is done under sedation or anaesthetic so you shouldn't feel it happening, though some cramping afterwards is common. Everyone's experience differs, so mention any concerns to your clinic.

How many eggs are needed for IVF to work?

There's no fixed number that guarantees success, because not every egg fertilises and not every embryo develops well. Your clinic can talk you through what's typical for someone with your ovarian reserve, based on your AMH and antral follicle count.

Do I need ICSI or standard IVF?

This depends mainly on sperm quality. ICSI, where a single sperm is injected into each egg, is often recommended when sperm count or movement is reduced, or after previous fertilisation problems. Your clinic will explain which applies to you.

Can IVF be done without any hormone injections?

Some clinics offer natural or mild stimulation cycles with lower doses of medication or none at all, but these typically produce fewer eggs. Whether this suits you depends on your individual situation, so it's worth discussing directly with your clinic.

How does IVF work?

Written by Zayn Miah & R KhanomLast updated 17 September 2026Not clinically reviewed

Short answer: IVF works by collecting eggs from the ovaries after hormone injections encourage several to mature at once, fertilising them with sperm in a lab, growing the resulting embryos for a few days, then placing one embryo back into the womb. Each stage is monitored closely by the clinic, and the exact plan depends on your own test results and history.

The basic idea

In a natural cycle your body usually releases one egg a month. IVF changes that by using hormone medication to encourage the ovaries to develop several eggs in one cycle, then collecting them before ovulation happens on its own. Fertilisation happens outside the body, in a lab dish, rather than inside the fallopian tube.

The four main stages

Ovarian stimulation: daily injections over roughly 8 to 14 days encourage multiple follicles to grow, with scans tracking progress.
Egg retrieval: a short procedure under sedation collects the eggs from the follicles using a fine needle guided by ultrasound.
Fertilisation: eggs are mixed with sperm, or a single sperm is injected into each egg (ICSI), and the lab checks the next morning for signs of fertilisation.
Embryo transfer: one embryo, occasionally two, is placed into the womb using a thin catheter, usually with no sedation needed.

Why the injections come first

Without stimulation medication, only one egg would usually be available. Having more eggs to work with increases the chances that at least one will fertilise and develop into a healthy embryo, though not every egg collected will fertilise or grow well, and that is expected rather than a sign anything has gone wrong.

What the scans are checking

Regular ultrasound scans during stimulation measure the size of the follicles and, alongside blood tests, help the clinic decide when the eggs are ready to be collected and when to give the trigger injection that causes final maturation.

What happens to the embryos

Embryos are grown in an incubator for between three and six days. The clinic will grade them based on appearance and development, and will discuss with you which one looks most likely to implant. Any suitable spare embryos can usually be frozen for future use.

No two cycles look identical. Your protocol, medication doses and number of eggs collected depend on your own ovarian reserve, age and how your body responds, so comparing your numbers to someone else's isn't a useful measure of how things are going.

After the transfer

Once the embryo is transferred, there is a wait of around ten to fourteen days before a blood or urine pregnancy test confirms whether implantation has happened. This is often called the two week wait and can be one of the hardest parts of the whole process emotionally.

What can vary between clinics

The exact stimulation protocol used, based on your hormone levels and history.
Whether ICSI or conventional insemination is used to fertilise the eggs.
Whether embryos are transferred fresh or frozen and transferred in a later cycle.
Whether additional tests like PGT-A are offered or recommended.

Questions worth asking your clinic

Which protocol will I be on, and why that one for me?
How many eggs would you expect me to produce?
Will you recommend ICSI, and if so, why?
What happens to any embryos we don't use this cycle?

Questions people ask next

Is IVF painful?: Most people find the injections cause mild stinging or bruising rather than significant pain. Egg retrieval is done under sedation or anaesthetic so you shouldn't feel it happening, though some cramping afterwards is common. Everyone's experience differs, so mention any concerns to your clinic.
How many eggs are needed for IVF to work?: There's no fixed number that guarantees success, because not every egg fertilises and not every embryo develops well. Your clinic can talk you through what's typical for someone with your ovarian reserve, based on your AMH and antral follicle count.
Do I need ICSI or standard IVF?: This depends mainly on sperm quality. ICSI, where a single sperm is injected into each egg, is often recommended when sperm count or movement is reduced, or after previous fertilisation problems. Your clinic will explain which applies to you.
Can IVF be done without any hormone injections?: Some clinics offer natural or mild stimulation cycles with lower doses of medication or none at all, but these typically produce fewer eggs. Whether this suits you depends on your individual situation, so it's worth discussing directly with your clinic.

Words on this page

Sources

IVF: what is IVF and how does it work?, HFEA (UK fertility regulator). Link checked 17 September 2026.
IVF overview, NHS. Link checked 17 September 2026.
Fertility problems: assessment and treatment (CG156), NICE. Link checked 17 September 2026.

Written by patients, not clinicians. This page has not yet been reviewed by a named fertility professional, so it explains published guidance and points you to the original source instead of giving medical advice. It is not medical advice. Decisions about your treatment belong with your own clinic. Read our editorial policy and corrections policy.