Most couples researching IVF understand it as a single process. In reality, it is five distinct clinical stages, each with its own timeline, biological demands, and set of variables that age influences differently. Understanding this before you travel for treatment is not just useful — it is the difference between arriving with realistic expectations and arriving with assumptions that the cycle will either shatter or confirm in ways that feel unexpected.
This guide walks through each of the 5 stages of IVF, explains exactly what happens, and maps precisely how age changes outcomes at every point, alongside how the team at Nova IVF Fertility Centre, Kolkata applies this understanding to personalise treatment for international patients.
Stage 1: Ovarian Stimulation
The first stage sets the foundation for everything that follows. Without an adequate number of mature eggs, the rest of the cycle has limited material to work with, and this is the stage where age creates the most visible and measurable difference between patients.
What Happens
Daily hormone injections, typically gonadotrophins containing FSH and LH, are administered for 8 to 14 days to stimulate the ovaries to produce multiple follicles simultaneously. Regular ultrasound scans and blood tests monitor follicle growth and oestrogen levels. When the lead follicles reach 17 to 20 mm, a trigger injection of hCG or a GnRH agonist is given to finalise egg maturation before retrieval 34 to 36 hours later. The protocol type (antagonist or long agonist) and the starting dose of gonadotrophins are adjusted individually based on AMH, antral follicle count, age, and body weight.
How Age Affects This Stage
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Under 35: Most patients produce 10 to 20 mature eggs per retrieval with standard stimulation. The ovaries are responsive, and the risk of over-stimulation (OHSS) in PCOS patients is higher. Protocol adjustment focuses on avoiding OHSS rather than maximising response.
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35 to 37: Response remains reasonable but begins to decline. Average egg yield drops to 8 to 14. Higher gonadotrophin doses are sometimes needed, and more monitoring appointments may be required.
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38 to 40: Diminished ovarian reserve becomes a significant factor. AMH and AFC decline, and stimulation may produce fewer follicles even at higher doses. Modified minimal stimulation or antagonist protocols are designed to retrieve what the ovaries can safely produce.
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Over 40: Egg yield is typically low, often two to five eggs per retrieval. Mini-IVF or sequential stimulation across back-to-back cycles may be used to accumulate enough embryos for chromosomal screening before transfer.
Nova IVF Fertility Centre, Kolkata tailors stimulation protocols specifically to each patient's ovarian reserve data. Patients over 38 undergo AMH and AFC assessment at the first consultation, and the protocol is designed around those numbers rather than a standard age bracket.
Stage 2: Egg Retrieval
Egg retrieval is a brief but technically precise procedure performed under sedation. The number and quality of eggs collected directly determines the range of embryos available at the subsequent stages, and age has a dual effect here reducing both quantity and quality simultaneously.
What Happens
A fine needle is passed through the vaginal wall under ultrasound guidance to aspirate the fluid from each follicle. The embryologist identifies and counts the eggs in the follicular fluid immediately. The procedure takes 20 to 30 minutes. Most patients are discharged within a few hours and rest for 24 to 48 hours.
How Age Affects This Stage
Egg maturity rate declines with age. In younger patients, 80 to 90 percent of retrieved eggs are mature and suitable for fertilisation. In patients over 40, this proportion can fall to 60 to 70 percent.
Egg quality, specifically the integrity of the spindle apparatus responsible for correct chromosomal segregation during fertilisation, deteriorates with age. This is not visible under the microscope at retrieval — it becomes apparent in the fertilisation and embryo development stages.
Poor ovarian response at this stage is not a signal to continue with the same protocol next time. It is clinical data that informs the protocol redesign for the subsequent cycle.
At Nova IVF Fertility Centre, Kolkata, the embryology team assesses maturity in real time and communicates with the patient immediately after retrieval, so the next steps are planned with full information about what was collected.
Stage 3: Fertilisation
Fertilisation is where eggs and sperm meet either through conventional insemination or ICSI — and where the male factor, often underestimated, becomes as important as the female factor. Age affects this stage primarily through egg quality, but sperm quality contributes independently.
What Happens
In conventional IVF, eggs are placed in a dish with prepared sperm and left to fertilise overnight. In ICSI (Intracytoplasmic Sperm Injection), a single sperm is selected by the embryologist and injected directly into each mature egg. ICSI is now the standard approach at most fertility centres for any degree of male factor infertility, and is also used when egg numbers are low to maximise the fertilisation of every available egg. Fertilisation is confirmed 16 to 18 hours after insemination or injection.
How Age Affects This Stage
Fertilisation rates themselves are broadly similar across age groups when ICSI is used, because the injection bypasses the natural fertilisation barrier.
However, age-related egg quality problems begin to manifest here. Eggs with compromised cytoplasmic integrity or spindle abnormalities may fail to fertilise even with ICSI, or may fertilise abnormally (polyspermy, degeneration).
Sperm DNA fragmentation, which affects fertilisation quality independently of age, is assessed at Nova IVF Fertility Centre, Kolkata alongside the female evaluation rather than as an afterthought. A high DFI in the male partner is addressed with PICSI or MACS sperm selection before ICSI.
| Male-factor scenario | Recommended approach at Nova IVF Kolkata |
|---|---|
| Normal semen parameters | Conventional IVF or ICSI based on egg number |
| Any degree of male factor | ICSI as standard |
| High sperm DNA fragmentation | PICSI or MACS selection before ICSI |
| Azoospermia | TESA or PESA coordinated same day as egg retrieval |
Stage 4: Embryo Development and Grading
The embryology laboratory is where the invisible impact of age becomes most visible. Embryos from younger eggs develop more reliably and reach blastocyst stage at higher rates. This stage is where the gap between age groups widens most dramatically.
What Happens
After fertilisation, embryos are cultured in the laboratory for three to five days. They are graded each day on their developmental stage and cell quality. The gold standard is reaching blastocyst stage on day 5 or 6, when the embryo has differentiated into an inner cell mass and trophectoderm. Blastocyst transfer produces higher implantation rates than day 3 cleavage stage transfer, and is now standard at Nova IVF Fertility Centre, Kolkata. Time-lapse imaging monitors embryo development continuously without disrupting incubation, with AI-assisted scoring helping embryologists identify the best candidate for transfer.
How Age Affects This Stage
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Under 35: 50 to 60 percent of fertilised eggs typically reach blastocyst stage, and the majority are chromosomally normal.
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35 to 38: Blastocyst rates begin to decline. More fertilised eggs arrest before day 5. The proportion with chromosomal abnormalities (aneuploidy) rises, often to 40 to 50 percent.
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Over 40: Blastocyst development rates can fall to 30 to 40 percent. Aneuploidy rates in resulting embryos exceed 70 to 80 percent, which is why PGT-A (Preimplantation Genetic Testing for Aneuploidy) is strongly recommended from age 37 to 38 onward.
PGT-A is available at Nova IVF Centre, Kolkata and is offered as a standard recommendation for patients over 37, for those with recurrent implantation failure, and for those who have experienced recurrent miscarriage.
Stage 5: Embryo Transfer and the Two-Week Wait
The final stage is where all the preceding work converges. One selected embryo is placed into the uterine cavity using a thin catheter. The procedure takes a few minutes and requires no anaesthesia. What follows the two-week wait for a pregnancy test — is both the most passive and most emotionally demanding part of the cycle.
What Happens
The embryo is transferred either fresh (on the day of stimulation cycle retrieval) or frozen (in a subsequent frozen embryo transfer cycle once the uterine lining is prepared separately). Frozen embryo transfer is now preferred in most cases because it allows the uterine environment to fully recover from stimulation, reduces OHSS risk, and allows time for PGT-A results when chromosomal testing has been done. The endometrium is prepared with oestrogen and progesterone support. ERA (Endometrial Receptivity Analysis) testing may be used for patients with recurrent implantation failure to identify the personalised progesterone exposure window.
How Age Affects This Stage
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Under 35: Implantation rates for good-quality blastocysts are 50 to 60 percent. The uterine environment is generally receptive with standard progesterone support.
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35 to 40: Implantation rates decline to 35 to 50 percent for untested embryos. With PGT-A, the rate per euploid embryo transfer recovers to comparable levels regardless of age, because the chromosomal barrier has been addressed.
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Over 40: Without testing, live birth rates per transfer drop below 15 to 20 percent. With a confirmed euploid embryo, live birth rates per transfer recover to 40 to 50 percent — the most compelling argument for PGT-A in older patients.
The two-week wait does not need to be spent at the fertility centre. Most international patients return home after transfer and receive their pregnancy test result remotely, with follow-up instructions from the Nova IVF Kolkata team.
Why Nova IVF Fertility Centre, Kolkata for International Patients
Nova IVF Fertility Centre, Kolkata brings together the complete clinical capability across all 5 stages of IVF within a single NABH-accredited programme, led by Dr. Aindri Sanyal (Clinical Director, FNB Reproductive Medicine, over 4,000 IVF cycles, ISAR Young Talent Award 2022) and supported by Dr. Rohit Gutgutia, Dr. Anindita Singh, Dr. Preeti Mahawar, and Dr. Suparna Bhattacharya.
Key advantages for international patients:
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AMH and sperm DNA fragmentation testing done concurrently at first consultation
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Time-lapse embryo monitoring and AI-assisted grading in the embryology lab
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PGT-A and ERA available on-site for patients who need them
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IVF treatment in India at Nova Kolkata costs Rs. 1,50,000 to Rs. 2,50,000 per cycle (USD 1,800 to USD 3,000) — 60 to 70 percent less than UK or USA equivalents
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Karetrip coordinates medical visa, accommodation near the centre, and post-transfer follow-up coordination with the patient's local OB at home
How Karetrip Connects International Patients to Nova IVF Centre, Kolkata
Every couple's position across the 5 stages of IVF depends on their specific AMH, sperm quality, embryo development history, and uterine factors — not just their age. Karetrip reviews each patient's existing investigations before recommending Nova IVF Kolkata, matching them with the IVF specialist whose expertise most closely fits their presentation, and coordinating every logistical element of the journey.
Chat with our Medical care assistant, RUA, for quick guidance and support and take the first step toward a personalised IVF programme at Nova IVF Centre, Kolkata.
Medical Disclaimer
This article is for informational purposes only and is not medical advice. IVF success rates and responses across all 5 stages depend heavily on your individual health markers (like AMH and semen quality), not just age. Always consult a certified fertility specialist before starting treatment.