What is IVF?

IVF = in vitro fertilisation. "In vitro" means outside the body. Normally: Egg + sperm → fertilisation in the fallopian tube → embryo → uterus With IVF, the first part happens in a laboratory: Egg retrieved from ovary + sperm → fertilisation in laboratory → embryo → uterus The embryo is then transferred into the uterus, where the goal is for it to implant and develop into a pregnancy. IVF is one of the most established forms of assisted reproductive technology and is used for a wide range of fertility problems.

Why would someone need IVF? You don't necessarily "need" IVF just because you're getting older or because you've frozen eggs. IVF is recommended when there is a reason that natural conception is unlikely, difficult, or when IVF offers a substantially better route to pregnancy. Some common reasons include: 1. Blocked or damaged fallopian tubes Normally, sperm needs to travel through the reproductive tract to meet the egg in the fallopian tube. If both tubes are blocked, the egg and sperm can't meet naturally. IVF bypasses the tubes completely: Ovary → egg retrieval → laboratory fertilisation → embryo → uterus Tubal disorders are one recognised cause of infertility.

2. Male-factor infertility This is particularly relevant given your previous question about sperm analysis. A man might have:

  • very low sperm concentration
  • poor sperm motility
  • abnormal sperm morphology
  • difficulty ejaculating
  • extremely low or absent sperm Depending on the severity, doctors may use ICSI. IVF vs ICSI These are often confused. IVF: Egg + thousands of prepared sperm → sperm fertilises egg naturally in the laboratory. ICSI: One sperm is selected and injected directly into the egg using a microscopic needle. ICSI is particularly useful when sperm quantity or function is significantly impaired.

3. Ovulation problems If someone isn't regularly releasing eggs, fertility medication may sometimes be enough. But if other treatments aren't successful, IVF can be used to stimulate the ovaries and retrieve eggs directly.

4. Endometriosis or other reproductive problems Endometriosis can interfere with fertility in several ways, and IVF may be considered depending on the severity, previous treatment and other factors.

5. Unexplained infertility Sometimes all the basic tests look reasonably normal but pregnancy doesn't occur. WHO estimates that infertility can result from male factors, female factors, a combination of factors, or remain unexplained. IVF can sometimes overcome some of the barriers that aren't identifiable through routine testing.

6. Age-related fertility decline This is especially relevant to the conversation we've been having. As women get older, egg quantity and egg quality decline. IVF doesn't reverse egg ageing. However, it allows doctors to retrieve multiple eggs in one cycle, rather than relying on the one egg normally selected and ovulated each month. That's one reason IVF becomes particularly relevant when someone is trying to maximise the opportunity for pregnancy at an older reproductive age.

7. Frozen eggs This is the connection to your previous question. If you freeze eggs at 35–38, for example, you can potentially use those eggs later. When you're ready: Frozen eggs ↓ thaw surviving eggs ↓ ICSI fertilised eggs ↓ embryo culture blastocyst ↓ embryo transfer pregnancy So egg freezing preserves the eggs; IVF is generally the process used later to try to make a baby from those eggs.

So how does IVF actually happen? Here's the whole process. Step 1 — Fertility assessment Before starting, the clinic generally evaluates both partners where applicable. For the woman, this can include:

  • AMH
  • AFC ultrasound
  • ovarian/uterine assessment
  • hormone tests
  • medical history For the man:
  • semen analysis
  • sometimes additional sperm testing The purpose is to determine what treatment makes sense and what kind of IVF protocol is appropriate.

Step 2 — Ovarian stimulation Normally, your body generally selects one dominant follicle during a menstrual cycle. With IVF, the goal is different. Doctors give hormonal medication to encourage multiple follicles to grow simultaneously. For example, instead of: 1 follicle → 1 egg you might have: 10 follicles → potentially several mature eggs The exact response varies significantly between women.

Step 3 — Monitoring During stimulation, you'll have several appointments. Typically: Ultrasound + blood tests → adjust medication → ultrasound + blood tests → adjust medication The doctor is watching:

  • follicle size
  • number of follicles
  • estrogen levels
  • ovarian response The goal is to retrieve a useful number of mature eggs while avoiding excessive stimulation.

Step 4 — The trigger injection Once enough follicles are appropriately developed, you'll receive a trigger injection. This helps the eggs complete their final maturation. The timing is extremely important because the egg retrieval is scheduled around the trigger.

Step 5 — Egg retrieval This is the procedure where the eggs are collected. The doctor uses an ultrasound-guided needle through the vagina and into the ovaries. The fluid from the follicles is aspirated and sent to the embryology laboratory, where embryologists identify the eggs. You're generally given sedation or anaesthesia, so you aren't experiencing the procedure in the normal way. The retrieval itself is usually relatively short.

Step 6 — The sperm sample On the same day, sperm is usually provided. The laboratory prepares the sperm by selecting a population with better characteristics for fertilisation. If sperm quality is adequate, conventional IVF may be used. If there is significant male-factor infertility, ICSI may be used instead.

Step 7 — Fertilisation This is where IVF gets its name. The eggs and sperm are brought together outside the body. If ICSI is used, an embryologist injects one sperm directly into each mature egg. Not every egg fertilises. ASRM notes that, on average, approximately 70% of mature eggs fertilise during IVF, although individual results vary. So imagine: 15 mature eggs ↓ approximately 10 may fertilise That's an illustration, not a prediction for you.

Step 8 — Embryo development The fertilised eggs are then cultured in the laboratory. They develop: Day 1: fertilised egg ↓ Day 2–3: dividing embryo ↓ Day 5–6: blastocyst This is another major point where numbers decrease. ASRM reports that approximately 50% of fertilised eggs develop to the blastocyst stage, although individual outcomes vary. So, purely as an illustration: 15 mature eggs ↓ 10 fertilised ↓ 5 blastocysts That doesn't mean you'll get exactly those numbers.

Step 9 — Genetic testing, sometimes Some embryos can undergo PGT-A (preimplantation genetic testing for aneuploidy). This involves taking a small sample of cells from the embryo and testing whether the embryo has the expected number of chromosomes. This can be particularly relevant when reproductive age is higher because chromosome abnormalities become more common with increasing egg age. However, PGT-A isn't automatically necessary or appropriate for everyone, and it does not guarantee a baby. A fertility specialist should explain whether it is useful in your particular circumstances.

Step 10 — Embryo transfer If there is an embryo suitable for transfer, it is placed into the uterus using a thin catheter. This is much less invasive than egg retrieval. The embryo is deposited inside the uterus. Then you wait.

Step 11 — The pregnancy test Approximately 10–14 days after embryo transfer, a blood test can determine whether implantation resulted in pregnancy. If positive, the clinic will generally monitor hormone levels and subsequently perform an ultrasound.

Here's the part that's really important IVF is not: "Take some eggs, fertilise them, and you're pregnant." There is a funnel. For example, imagine a hypothetical 38-year-old retrieves: 20 eggs ↓ 16 mature ↓ 11 fertilise ↓ 5 become blastocysts ↓ perhaps 2–3 are chromosomally normal ↓ one embryo is transferred ↓ pregnancy These numbers are illustrative only, not a prediction for a 38-year-old. The biological reason this matters is that you lose embryos at every stage. That's why doctors often talk about accumulating a sufficient number of eggs/embryos rather than assuming every egg will ultimately become a baby. ASRM specifically explains this "attrition" throughout the IVF process.

And this is where your age becomes important Suppose you freeze eggs at: 35 Then later use them at 40. The eggs retain the biological characteristics they had when they were frozen. So the relevant age for the egg's age-related chromosomal quality is primarily the age when the egg was retrieved. That's the fundamental reason egg freezing can be valuable. But there's another distinction: Egg freezing You're preserving potential. Embryo freezing You're preserving something further along the reproductive pathway. For example: Egg → fertilisation → embryo → blastocyst → frozen embryo You know more about that embryo than you know about an unfertilised egg. However, creating embryos requires sperm, which means embryo freezing is a different decision from egg freezing and can have relationship/donor implications.

Is IVF dangerous? IVF is generally considered a well-established and relatively safe medical procedure, but it isn't risk-free. One of the main medication-related complications is ovarian hyperstimulation syndrome (OHSS), where the ovaries respond excessively to stimulation. Modern protocols have substantially improved the ability to reduce this risk. There are also risks associated with:

  • egg retrieval
  • anaesthesia/sedation
  • ovarian stimulation
  • pregnancy itself
  • multiple pregnancy if more than one embryo is transferred Modern practice generally favours single-embryo transfer when appropriate because twin/multiple pregnancies carry higher obstetric risks.

IVF isn't necessarily the first step This is important. If you're healthy, ovulating regularly, your fallopian tubes are open, and your partner has a good semen analysis, you don't automatically need IVF. Treatment can progress from less invasive approaches to more complex treatments depending on the cause and circumstances. WHO's 2025 infertility guideline explicitly supports a stepwise approach to infertility care. It can look something like: Trying naturally ↓ fertility assessment ↓ ovulation treatment / timed intercourse ↓ IUI ↓ IVF ↓ ICSI / other specialised treatments The appropriate path depends on the underlying problem.

And for you specifically, there's an important distinction Based on the questions you've been asking about sperm analysis → egg freezing → IVF, you're essentially looking at the whole reproductive picture. I'd think about it as three separate pieces: 🥚 Egg side AMH + AFC + age → How many eggs might you have available? 🧬 Sperm side Semen analysis → How many sperm? How well do they move? What do they look like? 🧫 IVF side Egg + sperm → embryo → Can we create embryos and ultimately achieve a pregnancy? That's why fertility assessment is usually much more informative when both partners are evaluated, rather than assuming fertility is solely a female issue. WHO notes that infertility can arise from male factors, female factors, both, or remain unexplained. The easiest way to understand fertility in your 30s and early 40s is to separate three things that are often lumped together:

  • Egg quantity — how many eggs/follicles remain.
  • Egg quality — how likely an egg is to produce a chromosomally normal embryo.
  • Ability to conceive and carry a pregnancy — which depends on the eggs, sperm, uterus, tubes, ovulation and overall health. The important part is that age is much more strongly related to egg quality and reproductive success than AMH is. AMH and AFC are mainly useful for estimating how many eggs you might obtain during IVF/egg freezing. The big picture: 30 → 35 → 38 → 40 → 42 A conceptual illustration of the overall direction of natural fertility with age — not a prediction of any individual's probability of pregnancy:
  • Age 30 — generally high
  • Age 35 — still favourable for many women, but declining
  • Age 38 — decline becomes more significant
  • Age 40 — substantially lower; <10% pregnancy probability per cycle is an ACOG estimate
  • Age 42 — considerably reduced, though pregnancy remains possible

Fertility decline accelerates during the mid-to-late 30s; individual fertility varies substantially. Important: those values are deliberately conceptual, not clinical percentages. There isn't a scientifically valid single fertility percentage that applies to every 30-, 35-, 38-, 40- or 42-year-old woman. What we do know is that fertility begins declining around 30, declines more rapidly after the mid-30s, and by 40 relative fertility is roughly half that of women in their late 20s/early 30s.

🥚 Age 30 At 30, you are generally still in a relatively favourable reproductive period. You have:

  • a larger remaining follicle pool than you will later
  • generally better egg quality
  • lower rates of chromosomal abnormalities in embryos
  • relatively high natural conception rates ACOG estimates that healthy women in their 20s and early 30s have approximately a 25–30% chance of pregnancy in any individual menstrual cycle. That doesn't mean a 30-year-old has a 30% chance of having a baby every month. It's the probability of becoming pregnant during a cycle, and many factors influence it. Egg quality at 30 Most eggs are still relatively likely to have the correct chromosome complement. But here's something fascinating about egg ageing: Your eggs don't get created every month. You were born with the eggs you'll have throughout your reproductive life. The number declines continuously through follicular loss, and the remaining eggs age with you.

🥚 Age 35 35 is often talked about as if someone suddenly becomes infertile on their 35th birthday. That's not what happens. There isn't a biological cliff at 35. Instead, fertility is declining gradually, with the decline becoming more noticeable during the mid-30s and accelerating later. At 35, many women still conceive naturally without difficulty. But compared with 30, there is: ↓ egg quantity ↓ average egg quality ↑ chromosomal abnormalities ↑ miscarriage risk ↓ monthly probability of conception This is also the point at which doctors become more proactive about fertility evaluation. ASRM recommends infertility evaluation after 6 months of trying rather than 12 months for women aged 35 and older, assuming there isn't already a reason to investigate sooner.

🥚 Age 38 This is where I would start paying much more attention to fertility preservation if having biological children later is important to you. It's not because 38 is "too old." It's because the rate of change becomes increasingly significant. The two processes are happening simultaneously: Your ovarian reserve is decreasing You have fewer recruitable follicles. Your egg quality is decreasing A greater proportion of the remaining eggs have chromosome abnormalities. Those are two different processes. This is why someone can have a good AMH at 38 and still have age-related egg-quality problems. ASRM explicitly says ovarian-reserve markers such as AMH and AFC are useful for predicting egg yield during stimulation, but are poor predictors of reproductive potential independently of age.

🥚 Age 40 This is a major reproductive transition point. ACOG estimates that by age 40, the chance of pregnancy per menstrual cycle is less than 10%, compared with approximately 25–30% in healthy women in their 20s/early 30s. ASRM similarly describes relative fertility at 40 as approximately half that of women in their late 20s and early 30s. That doesn't mean: "You only have a 10% chance of ever having a baby." It means the probability of conception per cycle is considerably lower. And the chances of miscarriage and chromosomal abnormalities are higher. ACOG states that over age 40, approximately 1 in 3 pregnancies end in miscarriage, with most age-related early losses resulting from chromosome abnormalities.

🥚 Age 42 At 42, natural conception is still possible. But the biological odds are substantially different from 30–35. By this stage:

  • ovarian reserve is generally much lower
  • fewer eggs are available
  • the proportion of chromosomally abnormal eggs is much higher
  • conception takes longer on average
  • miscarriage risk is substantially higher
  • IVF using one's own eggs becomes less successful This is why ACOG recommends that women over 40 consider fertility evaluation before trying, rather than waiting six or twelve months.

🧬 The really important part: aneuploidy This is probably the most important scientific concept for understanding why age matters. Aneuploidy = an embryo has an abnormal number of chromosomes. A normal human egg should contain 23 chromosomes. After fertilisation: 23 from egg + 23 from sperm = 46 But as eggs age, errors during the final stages of meiosis become more common. This is called nondisjunction. It can occur during either Meiosis I or Meiosis II, the two cell divisions that produce a mature egg — in Anaphase I, for example, homologous chromosome pairs fail to separate properly. If chromosome separation goes wrong, an egg can end up with: 22 chromosomes or 24 chromosomes instead of 23. When that egg is fertilised, the resulting embryo may have an abnormal chromosome number. Some chromosomal abnormalities can result in conditions such as trisomy 21 (Down syndrome). Many others cannot develop normally and result in implantation failure or miscarriage. ACOG describes increasing maternal age as being associated with increasing aneuploidy and spontaneous abortion, likely because of errors in chromosome separation during meiosis.

How dramatic is the change? A recent large study of 9,385 blastocysts that underwent genetic testing found that the proportion of euploid (chromosomally normal) blastocysts declined progressively with age. The study found:

  • <30: ~74.5% euploid
  • ≥43: ~19.2% euploid The intermediate age groups, including 35–37, 38–40 and 41–42, showed progressive declines between those extremes. These figures should not be interpreted as your personal probability of having a normal embryo. The study involved embryos that had already reached the blastocyst stage and were selected for genetic testing, so it isn't the same thing as saying "74.5% of eggs are normal at 30." But it illustrates the biological principle extremely well: As egg age increases, the probability that an embryo will be chromosomally normal decreases.

🩸 And what happens to AMH? This is where things become slightly counterintuitive. AMH generally declines with age. That's because AMH is produced by small developing follicles, and the number of these follicles declines as ovarian reserve decreases. But women of the same age can have very different AMH levels. For example, two 38-year-olds could have: AMH 0.7 and AMH 3.5 respectively. The second woman may produce considerably more eggs during an IVF cycle. But it does not mean her eggs are biologically equivalent to those of a 30-year-old. That's the distinction: AMH → quantity/response Age → quality/reproductive potential

What about AFC? AFC = antral follicle count. An ultrasound counts small follicles in both ovaries. For example: Left = 6 Right = 7 AFC = 13 A higher AFC generally means you may have more follicles available to respond to IVF medication. But again: 13 follicles ≠ 13 high-quality eggs. AFC is mainly helping the fertility specialist estimate how your ovaries might respond to stimulation.

Here's a really useful way to picture it Imagine you have a basket of eggs. At 30: More eggs + higher average quality At 35: Fewer eggs + still generally good quality At 38: Fewer eggs + noticeably increasing chromosomal abnormality At 40: Fewer eggs + substantially higher chromosomal abnormality At 42: Fewer eggs + substantially higher chromosomal abnormality AMH tells you roughly: "How big is the basket?" Age tells you much more about: "What proportion of the eggs in the basket are likely to be capable of producing a chromosomally normal embryo?"

What does this mean for natural pregnancy? Very roughly: ACOG gives approximately 25–30% per cycle for healthy couples in their 20s/early 30s and <10% per cycle at 40. The exact number for 35, 38 or 42 varies considerably between studies and individuals, so I would be wary of anyone giving you a precise "you have X% chance this month" based only on age.

What happens to miscarriage risk? This is one of the biggest consequences of egg ageing. The main reason is chromosomal abnormality. As the percentage of chromosomally abnormal eggs/embryos rises: More abnormal embryos ↓ more implantation failure and/or more miscarriage ACOG estimates that about 1 in 3 pregnancies in women over 40 end in miscarriage, with chromosome abnormalities accounting for most of these early losses. So declining fertility isn't simply: "It's harder to get pregnant." It's also: "Even after getting pregnant, the probability of the pregnancy continuing is lower."

Now the interesting part: how egg freezing changes the picture This is where your earlier questions about egg freezing connect everything. Suppose you freeze eggs at 35. You then don't try for a baby until 41. Your body is 41. But the frozen eggs are still biologically 35-year-old eggs. That's the fundamental advantage. HFEA specifically reports that the age at which eggs are frozen has a major effect on subsequent success, whereas the age at thaw has much less impact on the egg itself. So: Scenario A Freeze at 35 → use at 41 The eggs were collected at 35. Scenario B Don't freeze → first try at 41 You're relying on eggs produced at 41. Those two situations are biologically different.

But egg freezing doesn't stop your biological clock This is extremely important. Freezing eggs at 35 doesn't mean: "I'm 35 forever." It preserves the eggs. It doesn't preserve:

  • your uterus
  • pregnancy-related health risks
  • your overall health
  • your future fertility
  • your partner's sperm
  • your ability to conceive naturally Pregnancy itself at an older age can carry increased risks, including gestational diabetes and hypertension/preeclampsia. So egg freezing is better thought of as: Preserving reproductive options — not freezing time.

And IVF changes the equation differently IVF allows you to control more steps. Instead of waiting every month for one egg: Hormonal stimulation ↓ multiple eggs retrieved ↓ fertilisation ↓ embryo development ↓ possibly genetic testing ↓ embryo transfer This can be particularly valuable when there is a fertility problem or when reproductive time is limited. But IVF doesn't make an older egg young again. If you undergo IVF at 42 using eggs retrieved at 42, those eggs still have the age-related chromosome risk of 42. That's why IVF success using a woman's own eggs generally declines with age. For example, UK 2024 data showed average birth rates per embryo transferred using patients' own eggs of 38% for ages 18–34, falling to 8% at ages 43–44.

This is why frozen eggs can be powerful Imagine: At 35 You retrieve 15 mature eggs. You freeze them. At 41 You decide you're ready. You don't have to rely exclusively on your 41-year-old eggs. You potentially have another pool of 35-year-old eggs available. The eggs are thawed, generally fertilised using ICSI, and developed into embryos. HFEA notes that most patients under 38 retrieves around 7–14 eggs per cycle, although individual results vary substantially. And this is why age at freezing is so important.

But there is a catch Egg freezing is not a guarantee. Suppose you freeze: 15 eggs You don't end up with 15 babies. Some eggs won't survive thawing. Some won't fertilise. Some embryos won't develop to blastocyst. Some blastocysts will be chromosomally abnormal. Some transfers won't implant. And some pregnancies will miscarry. That's the natural biological funnel. This is why the number of eggs frozen and the age at which they're frozen both matter. HFEA explicitly cautions that egg freezing should not be viewed as a guarantee of having a baby in the future.

If I were making a decision tree Age 30–34 → Usually plenty of time for many people → Egg freezing is an option, not necessarily something you need to do Age 35–37 → Start taking fertility planning more seriously → Consider AMH/AFC if future fertility preservation matters → If trying unsuccessfully, evaluate after 6 months Age 38–40 → Don't unnecessarily postpone evaluation → AMH + AFC can help estimate egg yield → If egg freezing is important to you, discuss it promptly → If trying naturally, don't wait a year before seeking help 40+ → Fertility assessment sooner rather than later → IVF may become relevant depending on circumstances → Egg freezing with one's own eggs becomes progressively less effective → Donor eggs may eventually become an option if own-egg IVF is unsuccessful ACOG recommends evaluation before trying for women over 40, while ASRM recommends earlier evaluation/treatment when appropriate for women 35 and older. The single most important takeaway Your AMH tells you more about how many eggs you may be able to retrieve. Your age tells you much more about the probability that those eggs will ultimately produce a healthy embryo and live birth. That's why a 38-year-old with excellent AMH isn't biologically equivalent to a 30-year-old with the same AMH.