IVF (In Vitro Fertilisation): How It Works, Steps, Risks and Success Factors
In vitro fertilisation (IVF) is a form of assisted reproductive technology in which eggs are collected from the ovaries and fertilisation is attempted in a laboratory. If embryos develop, one may be transferred into the uterus, where implantation can occur and pregnancy may continue.
IVF can be used for several causes of infertility, including some forms of tubal disease, male-factor infertility, endometriosis-associated infertility, ovulation problems and unexplained infertility. It may also be considered in some circumstances involving donor eggs or sperm.
But IVF is not one procedure with one predictable outcome. It is a sequence of steps, and the number of eggs, fertilised eggs, embryos and transferred embryos can change substantially along the way.
Understanding those stages helps explain why egg retrieval is not the same as fertilisation, embryo transfer is not the same as implantation, and a pregnancy rate is not the same as a live-birth rate.
WHO's 2025 infertility guideline emphasizes individualized, evidence-based fertility care and progression through treatment options according to clinical findings and patient preferences. IVF is therefore one possible treatment, not an automatic next step for everyone experiencing infertility.
What IVF Actually Changes
During natural conception, an egg and sperm generally meet in a fallopian tube. If fertilisation occurs, the early embryo travels toward the uterus.
IVF moves the fertilisation stage into a laboratory.
In simplified terms:
Natural conception
Ovulation → sperm and egg meet → fertilisation → embryo develops → embryo reaches uterus → possible implantation
IVF
Ovarian stimulation → egg retrieval → laboratory fertilisation → embryo development → embryo transfer → possible implantation
IVF can therefore bypass some problems involving the fallopian tubes.
It does not, however, bypass every factor involved in reproduction. Egg quality, sperm characteristics, embryo development, the uterine environment, age and other medical factors can still influence the outcome.
Who May Be Offered IVF?
IVF may be considered for several fertility problems, including:
Blocked or severely damaged fallopian tubes
Some forms of male-factor infertility
Certain cases of endometriosis-associated infertility
Some ovulation-related fertility problems
Unexplained infertility
Previous unsuccessful fertility treatment
Certain reproductive or genetic circumstances
Use of donor eggs or sperm when appropriate
Selected fertility-preservation circumstances
The appropriate treatment depends on the diagnosis.
Some people may be offered expectant management, ovulation treatment, surgery, intrauterine insemination (IUI) or another approach before IVF. Others may have circumstances in which IVF is considered earlier.
A fertility evaluation generally considers both reproductive partners when applicable. Female assessment can include ovulation, ovarian reserve when clinically useful, the uterus and fallopian tubes. Male assessment commonly includes semen analysis and further investigation when indicated.
The important question is therefore not simply:
"Can IVF treat this condition?"
It is:
"Is IVF the most appropriate treatment for this person's particular fertility situation?"
The IVF Process at a Glance
An IVF cycle commonly includes:
Treatment planning and baseline assessment
Ovarian stimulation
Ultrasound and other monitoring
Medication to control timing of ovulation
Triggering final egg maturation
Egg retrieval
Sperm preparation
Fertilisation
Embryo culture
Embryo assessment and, when appropriate, genetic testing
Fresh or frozen embryo transfer
Pregnancy testing and follow-up
Not every cycle follows exactly the same sequence.
Some patients have embryos frozen for later transfer rather than having a fresh transfer. Additional procedures may or may not be appropriate.
Step 1: Planning and Preparation
Before treatment begins, the fertility team reviews medical and reproductive history and determines whether IVF is appropriate.
Depending on the situation, evaluation may include:
Menstrual and reproductive history
Previous pregnancies and fertility treatments
Ovarian reserve assessment
Ultrasound
Assessment of the uterus and fallopian tubes when appropriate
Semen analysis
Review of medical conditions
Medication review
Infectious-disease testing where required
Other investigations based on the diagnosis
This stage matters because IVF does not correct every cause of infertility.
The treatment protocol may also be influenced by age, ovarian reserve, previous treatment response and the clinic's approach.
Step 2: Ovarian Stimulation
In a natural cycle, usually one follicle becomes dominant and releases an egg.
During IVF, fertility medicines are generally used to stimulate the ovaries so that several follicles develop.
The objective is not simply to produce "as many eggs as possible." The aim is to obtain a useful group of mature eggs while minimizing treatment-related complications.
During stimulation, the clinic may use:
Ultrasound examinations
Blood tests
Medication adjustments
Patients may need several monitoring appointments.
The exact protocol varies. Some medicines stimulate follicle development, while others are used to prevent premature ovulation.
Why Do the Numbers Change?
One of the most important concepts in IVF is that the numbers do not remain constant.
For example:
Follicles do not equal eggs.
Retrieved eggs do not equal mature eggs.
Mature eggs do not equal fertilised eggs.
Fertilised eggs do not equal transferable embryos.
Transferred embryos do not equal pregnancies.
This natural attrition is one reason why an early treatment number should not be interpreted as a guaranteed outcome.
Step 3: Triggering Final Egg Maturation
When monitoring shows that the follicles have reached an appropriate stage, the fertility team may prescribe a medication known as a trigger.
The trigger helps coordinate final egg maturation and the timing of egg retrieval.
Timing matters because the retrieval is scheduled around the expected maturation window.
Patients should follow the clinic's instructions precisely rather than adjusting the trigger time themselves.
Step 4: Egg Retrieval
Egg retrieval, also called oocyte retrieval, is used to collect eggs from the ovaries.
The procedure is generally performed using ultrasound guidance. A thin needle is passed through the vaginal wall toward the ovarian follicles, and follicular fluid is collected for laboratory examination.
Sedation or pain-relief medication is commonly used according to the clinic and patient's circumstances.
Afterward, temporary symptoms may include:
Pelvic discomfort
Cramping
Bloating
Tiredness
Light vaginal bleeding
The clinic should provide individual instructions about activity, medicines and warning signs after the procedure.
Although egg retrieval is generally considered a routine fertility procedure, complications can occur. Significant bleeding, severe pain, fever, fainting, breathing difficulty or other concerning symptoms should be reported promptly.
Step 5: Sperm Collection and Preparation
Sperm may be provided by a partner or donor, depending on the treatment plan.
The laboratory prepares the sample for fertilisation.
Semen analysis may assess characteristics such as:
Sperm concentration
Motility
Morphology
The results can help the fertility team decide whether conventional IVF or ICSI is appropriate.
Step 6: Fertilisation — Conventional IVF or ICSI
There are two important laboratory approaches.
Conventional IVF
Prepared sperm and eggs are placed together under controlled laboratory conditions so that fertilisation can occur.
ICSI
Intracytoplasmic sperm injection (ICSI) involves injecting a single sperm directly into an egg.
ICSI may be useful in selected circumstances, particularly some forms of significant male-factor infertility or when previous fertilisation has been unsuccessful.
However, ICSI should not automatically be viewed as a more powerful version of IVF.
Whether it adds value depends on the patient's circumstances and the reason IVF is being performed.
The fertility team should be able to explain why ICSI is or is not being recommended.
Step 7: Embryo Development
After fertilisation, embryos are cultured in the laboratory.
Embryologists monitor their development over the following days.
Not every fertilised egg continues developing normally.
Some embryos stop developing, while others reach stages at which they may be considered for transfer or freezing.
This is another reason why a retrieved-egg number cannot be used as a direct estimate of the eventual number of embryos available.
Step 8: Embryo Assessment and Genetic Testing
Embryologists evaluate embryo development using laboratory criteria.
Embryo morphology and developmental stage can contribute to transfer decisions, but appearance alone cannot guarantee implantation or live birth.
What Is PGT?
Preimplantation genetic testing (PGT) refers to genetic testing performed on embryos before transfer.
Different forms of PGT address different questions.
For example:
PGT-M can be used when testing for a specific inherited single-gene condition.
PGT-A evaluates chromosome number.
PGT is not one universal test, and it is not appropriate or necessary for every IVF cycle.
In particular, ASRM's 2024 committee opinion states that the value of PGT-A as a routine screening test for all patients undergoing IVF has not been established. Evidence from randomized trials has not demonstrated a universal improvement in live-birth outcomes.
Patients considering PGT should discuss:
Why the test is being proposed
What condition it is intended to investigate
What the test can and cannot determine
The possibility of an inconclusive or mosaic result
Costs
How results could affect embryo-transfer decisions
Whether genetic counseling is appropriate
Genetic testing should therefore be treated as an individualized decision rather than an automatic IVF add-on.
Step 9: Fresh or Frozen Embryo Transfer
Once an embryo is considered suitable for transfer, the fertility team decides when transfer should occur.
Fresh embryo transfer
The embryo is transferred during the same general treatment cycle as egg retrieval.
Frozen embryo transfer
An embryo that was previously frozen is thawed and transferred during a later cycle.
A frozen transfer does not necessarily mean that the original IVF cycle failed. Embryos may be intentionally frozen because a later transfer is considered more appropriate.
The choice can depend on hormone levels, uterine conditions, embryo availability, treatment protocol and individual circumstances.
Embryo Transfer Is Not Implantation
These two terms describe different events.
Embryo transfer is a medical procedure in which an embryo is placed inside the uterus.
Implantation is a biological process that may occur after transfer when the embryo attaches to the uterine lining.
Therefore:
Transfer ≠ implantation
and
implantation ≠ guaranteed ongoing pregnancy.
The embryo must continue developing and the pregnancy must progress normally after implantation.
How Many Embryos Are Transferred?
The number of embryos transferred is an important safety decision.
Transferring multiple embryos can increase the likelihood of multiple pregnancy, which carries additional risks for both the pregnant person and babies.
For appropriate patients, transferring a single embryo can substantially reduce the risk of multiple pregnancy.
ASRM identifies single-embryo transfer as an important strategy for reducing multiple gestation.
The appropriate number depends on factors such as:
Age
Embryo development
Previous IVF history
Embryo testing
Medical circumstances
Applicable professional guidance
Patients should ask their fertility team why a particular transfer strategy is being recommended.
What Happens After Embryo Transfer?
After transfer, the embryo must implant for pregnancy to develop.
The clinic will tell you when to perform a pregnancy test. Testing too early can be misleading because pregnancy hormone levels may not yet be detectable at a reliable level.
If the test is positive, follow-up may include blood testing and ultrasound at an appropriate stage.
A positive pregnancy test confirms a pregnancy-related hormonal signal, but it does not establish that the pregnancy will continue normally.
The fertility team will explain the next steps.
How Should IVF Success Rates Be Understood?
"IVF success rate" is not a single number.
A clinic might report:
Pregnancy rate
Clinical pregnancy rate
Live-birth rate
Rate per embryo transfer
Rate per egg retrieval
Cumulative live-birth rate
These measures answer different questions.
CDC ART reporting distinguishes outcomes by measures such as intended retrieval, actual retrieval and transfer, and cumulative outcomes can include transfers occurring after an egg retrieval over a defined period.
Therefore, comparing a clinic's "success rate" with another clinic's number without checking the definition can produce a misleading impression.
Questions to ask about a success statistic
When looking at IVF statistics, ask:
Is this pregnancy or live birth?
Is it calculated per retrieval or per transfer?
Does it include all patients or only a selected group?
Are donor eggs included?
What age groups are represented?
Is the figure cumulative?
What year does the data represent?
CDC specifically cautions that average ART success rates may not reflect the actual outcome for an individual or couple.
What Factors Can Affect IVF Outcomes?
No single factor determines the outcome.
Age
Age is an important factor because reproductive potential, particularly egg quantity and egg quality, generally changes with age.
Ovarian reserve
Tests such as AMH and antral follicle count can provide information about ovarian reserve and expected response to stimulation.
However, ovarian-reserve testing does not directly measure egg quality and should not be interpreted as an individual guarantee of IVF success.
Sperm factors
Sperm concentration, motility, morphology and other reproductive factors can affect fertilisation and treatment decisions.
Embryo development
Even when fertilisation occurs, not every embryo continues developing normally.
Uterine and reproductive factors
The uterus, uterine cavity and other reproductive conditions can influence implantation and pregnancy.
Medical history and previous treatment
Previous IVF results, underlying medical conditions and treatment response can help clinicians adjust future treatment.
These factors interact. That is why an individualized estimate from a fertility specialist is more informative than applying a single online percentage to every patient.
Important IVF Risks
IVF is an established medical treatment, but it is not risk-free.
Medication side effects
Stimulation medicines can cause symptoms such as:
Bloating
Abdominal discomfort
Headache
Breast tenderness
Injection-site reactions
Mood changes
The exact effects depend on the medications used.
Ovarian hyperstimulation syndrome
Ovarian hyperstimulation syndrome (OHSS) occurs when the ovaries respond excessively to stimulation.
Mild forms can cause bloating and abdominal discomfort. More severe disease can involve substantial fluid shifts and other complications.
Modern stimulation strategies can reduce risk, but OHSS remains an important complication to discuss with the fertility team.
Contact the clinic promptly if you develop significant abdominal swelling or pain, repeated vomiting, marked weakness, shortness of breath, reduced urination or rapidly worsening symptoms after stimulation or egg retrieval.
Egg-retrieval complications
Rare complications can include:
Bleeding
Infection
Injury to nearby structures
Complications related to sedation or anesthesia
Your clinic should explain procedure-specific risks before treatment.
Multiple pregnancy
Multiple pregnancy is more likely when more than one embryo is transferred.
Twin and higher-order pregnancies have increased risks, including preterm birth and other pregnancy complications.
This is one reason embryo-transfer strategy is an important part of IVF safety.
Emotional and financial burden
IVF can involve repeated appointments, injections, procedures, waiting periods and uncertainty.
People may experience:
Anxiety
Disappointment
Treatment fatigue
Relationship stress
Financial pressure
Fear about treatment failure
Psychological support can be a useful part of fertility care. Seeking counseling does not mean that someone is coping poorly; fertility treatment can be genuinely demanding.
WHO's current infertility guidance also emphasizes psychosocial support as part of comprehensive infertility care.
What If an IVF Cycle Does Not Work?
An unsuccessful cycle does not by itself establish that future pregnancy is impossible.
The fertility team may review:
Response to stimulation
Number of eggs retrieved
Egg maturity
Fertilisation
Embryo development
Number and quality of embryos
Transfer details
Uterine factors
Sperm findings
Medication response
Depending on those findings, possible next steps could include another treatment cycle, a modified protocol, additional evaluation, another fertility treatment or stopping treatment.
Another IVF cycle is not automatically the right choice.
The decision should consider medical circumstances, expected benefit, treatment burden, finances, emotional wellbeing and the person's reproductive goals.
IVF and Blocked Fallopian Tubes
Blocked or severely damaged fallopian tubes are an important reason IVF may be considered.
IVF can bypass the point at which sperm and egg would normally need to meet inside the tube.
However, the presence of a blocked tube does not automatically mean IVF is required in every case.
The treatment decision can depend on:
Whether one or both tubes are affected
The condition of the remaining tube
Age
Ovarian reserve
Duration of infertility
Sperm factors
Other reproductive conditions
A particular tubal condition called hydrosalpinx, in which a blocked tube becomes filled with fluid, may require specific assessment before embryo transfer.
The appropriate management should be determined by the fertility specialist rather than by the diagnosis alone.
IVF and Male-Factor Infertility
Infertility can involve male factors, female factors, both partners or no clearly identifiable cause.
Male-factor infertility can influence whether conventional IVF, ICSI, sperm retrieval or another treatment is considered.
ICSI may be particularly relevant when sperm-related factors make conventional fertilisation difficult.
This is another reason IVF should not be described as a treatment exclusively for women. Fertility treatment decisions should consider both partners when applicable.
What About Lifestyle and IVF?
Healthy lifestyle habits are useful for general health, but no diet, exercise routine, herb or supplement can guarantee IVF success.
Discuss with your fertility team:
Smoking
Alcohol
Recreational drugs
Prescription medicines
Over-the-counter medicines
Supplements
Herbal products
Existing medical conditions
Nutrition
Physical activity
Avoid products marketed as "fertility boosters" simply because they are described as natural.
Evidence for many fertility supplements is limited or inconsistent, and some products may interact with medicines or be unsuitable during fertility treatment.
Questions to Ask Before Starting IVF
Before beginning treatment, useful questions include:
About the reason for treatment
Why is IVF being recommended in my situation?
Are there reasonable alternatives?
What is the likely cause of infertility?
Does my partner need additional evaluation?
About the treatment cycle
Which stimulation protocol is being proposed?
How will my response be monitored?
What are my individual risks of OHSS?
What happens if I respond too strongly or too weakly?
About the laboratory
Will conventional IVF or ICSI be used?
If ICSI is recommended, what is the specific reason?
How are embryos assessed?
Is PGT being recommended? If so, what question is it intended to answer?
About embryo transfer
Is a fresh or frozen transfer planned?
Why?
How many embryos are recommended for transfer?
What are the risks of multiple pregnancy?
About outcomes
How is the clinic's success rate calculated?
Is it a pregnancy rate or live-birth rate?
Is it reported per retrieval or transfer?
How does my age and medical history affect the estimate?
About costs and next steps
What is included in the quoted treatment cost?
Which medicines and laboratory procedures cost extra?
What happens if the cycle produces no transferable embryo?
What would you review if the cycle is unsuccessful?
What additional costs could arise from another cycle or testing?
These questions can make the treatment plan clearer and help patients understand which decisions are individualized.
Key Takeaways
IVF is a sequence of fertility-treatment stages rather than a single procedure.
Fertilisation occurs in the laboratory; pregnancy develops in the uterus after embryo transfer.
IVF can bypass certain fallopian-tube problems but does not bypass every cause of infertility.
Eggs retrieved, fertilised eggs, embryos and transferred embryos are different stages and should not be treated as interchangeable numbers.
ICSI involves injecting one sperm directly into an egg and is used selectively rather than automatically for every IVF cycle.
PGT is not one test, and PGT-A has not been established as a universally beneficial screening test for every IVF patient.
Embryo transfer does not guarantee implantation or an ongoing pregnancy.
IVF success statistics must be interpreted according to age, diagnosis, treatment type and the denominator used.
IVF has potential risks, including OHSS, egg-retrieval complications and multiple pregnancy.
A failed cycle does not automatically mean that future treatment cannot result in pregnancy.
Treatment choices should be based on the individual's diagnosis, medical circumstances, reproductive goals, expected benefits, risks and treatment burden.
Medical Disclaimer
This article provides general educational information and does not replace individualized medical advice, diagnosis or treatment. IVF protocols, fertility medications, laboratory procedures, testing options and treatment outcomes vary between individuals and clinics. Do not start, stop or change fertility medicines, supplements or other treatments based solely on this article. Anyone considering IVF should discuss the potential benefits, risks, alternatives, costs and expected outcomes with a qualified fertility specialist. Seek prompt medical attention for severe pain, heavy bleeding, breathing difficulty, fainting, rapidly worsening abdominal swelling or other potentially serious symptoms during or after fertility treatment.
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