IVF explained: what happens at each stage and what to realistically expect

Trying to conceive · Updated July 2026 · All articles

What IVF actually involves: a brief overview

In vitro fertilisation (IVF) is a process in which eggs are collected from the ovaries, fertilised by sperm in a laboratory, and one or more of the resulting embryos are transferred back into the uterus. The name comes from the Latin for "in glass": fertilisation takes place outside the body, in a controlled laboratory environment, rather than in the fallopian tube as it does naturally.

The full process spans several weeks and involves multiple stages, each with its own set of procedures, monitoring appointments and potential anxieties. Many people find that the process feels more manageable once they understand what is happening at each stage, because the uncertainty of not knowing what to expect is often more stressful than the reality of going through it.

IVF is recommended when natural conception is unlikely due to tubal factors, severe male factor infertility, failure of simpler treatments like IUI, significant endometriosis, very low ovarian reserve, or after extended unexplained infertility. It is a significant undertaking, physically and emotionally, and going in with realistic expectations is one of the most useful things you can do.

Stage one: ovarian stimulation

The first active stage of IVF is ovarian stimulation: giving the ovaries hormonal medication to encourage multiple follicles (fluid-filled sacs containing eggs) to develop simultaneously. In a natural cycle, only one dominant follicle usually develops. IVF aims to retrieve multiple eggs in a single collection to maximise the chances of having good-quality embryos to work with.

Stimulation typically uses injectable gonadotrophins, which you self-administer daily (usually into the abdomen) for 10 to 14 days. The injections are not usually painful, though there can be stinging and bruising at the injection site. You will attend the clinic for monitoring scans and blood tests every two to three days throughout this phase so the team can track follicle growth and adjust your dose if needed.

Common side effects during stimulation include bloating (the ovaries enlarge as follicles develop), breast tenderness, fatigue and mood changes. Ovarian hyperstimulation syndrome (OHSS), where the ovaries over-respond to medication, is a risk, particularly for people with a high antral follicle count or PCOS. Mild OHSS is common and manageable; severe OHSS is rare but serious, and modern protocols are designed to minimise the risk.

Stage two: egg collection

When follicles reach the right size (usually 17 to 20 mm), a trigger injection is given to mature the eggs. Egg collection happens approximately 36 hours later. It is a day-case procedure done under sedation or light anaesthesia, though some clinics do it with local anaesthetic only.

Using transvaginal ultrasound guidance, a needle is passed through the vaginal wall into each follicle to aspirate the fluid. The embryologist checks the fluid under a microscope immediately and identifies any eggs present. The whole procedure takes around 20 to 30 minutes. Afterwards you will feel crampy and groggy from the sedation, and most people rest at the clinic for an hour or so before going home.

The number of eggs collected varies widely depending on your ovarian reserve and how well you responded to stimulation. A typical collection might yield 8 to 15 eggs, though this varies considerably. Not all eggs will be mature, and not all mature eggs will fertilise: these attrition rates are normal and expected at every stage of the process.

Stage three: fertilisation and embryo culture

After collection, mature eggs are either mixed with prepared sperm (conventional IVF) or individually injected with a single sperm (ICSI). Fertilisation is checked the following morning: a fertilised egg at this stage is called a zygote. Not all eggs will fertilise, and you will usually receive a call from the embryology team on the morning after collection with an update on how many fertilised.

Fertilised eggs are cultured in an incubator for three to five days, developing from zygotes to two-cell embryos, through a four-to-eight-cell stage, to blastocysts (day 5 or 6 embryos with a differentiated inner cell mass and trophectoderm). Not all fertilised eggs will make it to blastocyst stage: this is another point of natural attrition. In a typical cycle, around 40 to 60 percent of fertilised eggs may reach blastocyst stage.

Blastocysts are the preferred stage for transfer because their development to that point selects for embryos with better viability. However, not every clinic and not every cycle will produce blastocysts, and transferring at day 3 (cleavage stage) is also valid, particularly when fewer embryos are available. The embryology team will advise on the right timing for your cycle.

Stage four: embryo transfer

Embryo transfer is a brief outpatient procedure with no anaesthesia required. One or more embryos are loaded into a fine catheter and placed into the uterus through the cervix under ultrasound guidance. It usually takes around 10 minutes and feels similar to a smear test. Most people experience minimal discomfort.

Current best practice in most UK clinics is to transfer a single embryo (elective single embryo transfer, eSET) in order to minimise the risk of twins or higher-order pregnancies, which carry significantly higher risks for both the mother and babies. Multiple embryo transfer is occasionally considered in specific circumstances, but it is not the default recommendation in reputable clinics following HFEA guidance.

After transfer, the two-week wait begins. This is widely described as the most emotionally difficult part of an IVF cycle, and for good reason: there is nothing more to do, and the outcome is beyond anyone's control. Progesterone support (pessaries or injections) is usually prescribed to support the luteal phase and early pregnancy until the pregnancy test date.

Frozen embryo transfer: often the better option

If more embryos develop than are needed for an immediate transfer, good-quality surplus embryos can be frozen (vitrified) for use in future cycles without going through stimulation and collection again. Frozen embryo transfer (FET) is increasingly common and has become the dominant approach in many clinics.

There are circumstances where freezing all embryos and doing a FET in a subsequent cycle is recommended. These include elevated progesterone at the end of stimulation (which may reduce endometrial receptivity), a high risk of OHSS (freezing avoids the additional hormonal burden of fresh transfer), and in cycles where preimplantation genetic testing (PGT) is being done.

FET cycles are typically shorter and less physically demanding than fresh cycles. The uterus is prepared with either natural cycle monitoring or estrogen and progesterone medication, and transfer is timed to the appropriate point. Success rates for frozen embryo transfers are broadly comparable to fresh transfers in most patient groups, and in some situations, particularly where the endometrium needs time to recover, FET can outperform a fresh transfer.

Success rates by age: the real numbers

IVF success rates vary significantly by age, and it is worth knowing the realistic figures rather than the optimistic ones. According to HFEA data, the live birth rate per embryo transfer for women using their own eggs is approximately 29 to 32 percent for those under 35, around 25 percent for ages 35 to 37, 18 to 20 percent for ages 38 to 39, and 10 to 12 percent for ages 40 to 42. Above 42, rates fall further.

These figures are per cycle. Cumulative success rates across multiple cycles are meaningfully higher: over three complete cycles (including FETs from the same egg collection), success rates of around 60 to 65 percent have been reported for women under 35. Understanding this distinction between per-cycle and cumulative rates is important when you are weighing up the overall process.

Clinics are required to publish their success rates via the HFEA register in the UK. When comparing clinics, look at live birth rates per embryo transfer for your age group, and take into account the type of patients each clinic treats. A clinic with very high published rates may have a more selective patient intake; a clinic that takes more complex cases may show lower published rates while actually offering better individualised care.

ICSI and preimplantation genetic testing

ICSI (intracytoplasmic sperm injection) is a variant of IVF in which a single sperm is injected directly into each mature egg rather than allowing fertilisation to occur naturally in the dish. It is used when sperm count, motility or morphology is significantly impaired, when previous IVF cycles had poor fertilisation rates, or when sperm has been surgically retrieved from the testis or epididymis. ICSI does not necessarily improve pregnancy rates over conventional IVF when sperm quality is normal.

Preimplantation genetic testing (PGT) involves taking a small biopsy from a blastocyst embryo before transfer and analysing the chromosomes or specific genetic sequences. PGT-A (testing for chromosomal abnormalities) can identify embryos with the correct number of chromosomes, which are more likely to implant and less likely to miscarry. PGT-M tests for specific inherited single-gene conditions. Both require all embryos to be frozen while results are awaited.

PGT is not universally recommended and adds significant cost. It is most often considered for people with recurrent implantation failure, recurrent miscarriage, advanced maternal age, or a known genetic condition in the family. The decision whether PGT is appropriate for your situation is worth discussing in detail with your fertility team.

Preparing emotionally for your first cycle

IVF is simultaneously a medical procedure and one of the more emotionally demanding experiences many people will ever go through. The combination of physical symptoms, invasive monitoring, financial pressure, uncertainty and hope makes it genuinely hard, and it is worth naming that rather than expecting yourself to be stoic about it.

A few things tend to help people navigate it better. Setting up your support in advance, whether that is telling close family or friends, engaging a counsellor, or finding an online community of others going through IVF at the same time, means you are not building that support from scratch while also doing the cycle. Being honest with your partner about how each of you is likely to cope and what you each need avoids misaligned expectations that add friction during an already pressured time.

Going in with realistic expectations is protective rather than pessimistic. Knowing that even a successful cycle can take two or three attempts, that embryo loss at various stages is statistically normal, and that the two-week wait is hard for everyone does not reduce your hope; it reduces the chance that a specific setback will feel like a catastrophic surprise rather than an understood part of the process. Many people who eventually succeed at IVF say that the cycles that did not work were still part of the journey, not wasted time.

Frequently asked questions

What is the difference between IVF and ICSI?

In standard IVF, eggs and sperm are placed together in a dish and fertilisation happens naturally. In ICSI, a single sperm is injected directly into each egg. ICSI is used when sperm quality is significantly impaired or when previous IVF had poor fertilisation. It does not necessarily improve outcomes when sperm quality is normal.

What are the IVF success rates for women under 35?

According to HFEA data, the live birth rate per embryo transfer for women under 35 using their own eggs is approximately 29 to 32 percent. Cumulative rates across three cycles are higher, around 60 to 65 percent in some analyses. Rates decline progressively with age from 35 onwards.

Is a frozen embryo transfer better than a fresh transfer?

Not always, but in some circumstances yes. FET allows the uterus to recover from stimulation and may result in a more receptive endometrium. For people with high follicle counts or OHSS risk, freezing all embryos is standard practice. Success rates for FET are broadly comparable to fresh transfers in most patient groups.

How many embryos should be transferred?

Current best practice is to transfer a single embryo (eSET), which significantly reduces the risk of multiple pregnancy. Multiple pregnancies carry higher risks for both mother and babies. Multiple embryo transfer is occasionally considered in specific circumstances after discussion with the medical team.

What is the stimulation phase like?

Ovarian stimulation typically lasts 10 to 14 days. You self-inject gonadotrophin medication daily and attend the clinic every 2 to 3 days for monitoring scans and blood tests. Common side effects include bloating, breast tenderness, fatigue and mood changes. Severe OHSS is rare but is monitored for throughout.

How long does a full IVF cycle take?

A fresh cycle from stimulation start to pregnancy test takes approximately 4 to 6 weeks. A frozen embryo transfer cycle adds another 4 to 6 weeks. Including preparation and pre-treatment medication, the full cycle from first consultation to result can span 2 to 3 months.

This article is for general information only. If you have concerns about your fertility or reproductive health, speak to your GP or a fertility specialist.