The In Vitro Fertilization (IVF) program is an assisted reproductive technology procedure that involves a series of highly controlled clinical and laboratory stages. The success of this program depends on precise synchronization between the patient’s physical preparation and the handling of eggs and sperm in the embryology laboratory. Understanding each phase helps minimize the risk of cycle cancellation and optimizes the chances of success.
Stage 1: Follicle Preparation and Synchronization via Estrogen Priming
Before ovarian stimulation begins, initial preparation is required to ensure that antral follicles (small fluid-filled sacs in the ovaries, each containing one immature egg) grow uniformly. This preparation process is called estrogen priming—the administration of the estrogen hormone prior to stimulation to synchronize the condition of the follicles in the ovaries so they develop simultaneously, typically lasting one to three weeks.
If using estrogen tablets or patches, therapy begins a few days after ovulation is confirmed via a urine test kit or hormonal blood test. If using oral contraceptives, therapy starts on the first day of menstruation. This step ensures the ovaries are in a resting state without any follicle growing ahead of the others.
Stage 2: Controlled Ovarian Stimulation and Hormonal Monitoring
Active stimulation begins after the initial evaluation shows the uterus is ready, the endometrium (the inner lining of the uterus that thickens each month to prepare for pregnancy) is thin, and there are no functional cysts (fluid-filled sacs that form naturally in the ovaries during the menstrual cycle and can interfere with stimulation if they have not resolved). The patient then receives daily injections of gonadotropins (hormones that stimulate the ovaries to produce multiple eggs at once, containing FSH and LH), unlike a natural cycle which typically matures only a single follicle.
During the 8–12 days of stimulation, the patient undergoes 4–6 monitoring sessions via transvaginal ultrasound to measure follicle diameter and endometrial thickness, as well as blood tests to monitor estradiol (the main estrogen hormone reflecting follicular development) and progesterone levels.
To prevent premature ovulation due to a natural LH surge, a GnRH antagonist or agonist injection is added—medications that temporarily halt hormonal signals from the brain so ovulation does not occur prematurely. When the follicles reach mature size, a trigger shot is administered using hCG (human Chorionic Gonadotropin) or a GnRH agonist—an injection that triggers the final maturation of the eggs. Egg retrieval must be scheduled 34–36 hours after the trigger shot, right before natural ovulation occurs.
The risk of cycle cancellation before egg retrieval can reach 20% in certain populations, generally caused by being a poor responder (the ovaries do not respond well to stimulation, producing too few follicles)—which occurs more frequently in women over 35—premature LH surge, or an extreme ovarian response that risks triggering OHSS (Ovarian Hyperstimulation Syndrome, a condition where the ovaries overreact to stimulation hormones, causing them to swell and fluid to accumulate in the abdomen).
Stage 3: Egg Retrieval and Post-Operative Recovery
The egg retrieval procedure is performed under intravenous sedation—anesthesia administered through a vein to induce a light sleep during the procedure. Guided by transvaginal ultrasound, an aspiration needle is directed through the vaginal wall straight into the follicles (fluid-filled sacs in the ovary containing the eggs) to suction the follicular fluid. This fluid is immediately handed over to the embryologist in the laboratory to identify the eggs.
After the procedure, the patient is monitored for 60–90 minutes before being discharged. Side effects such as mild abdominal cramping, bloating, and constipation are common for about a week. The patient is advised to drink 8–12 glasses of water or electrolyte-rich fluids daily and increase fiber intake. Strenuous physical activity and sexual intercourse should be avoided for two weeks to prevent ovarian torsion—a condition where the enlarged ovary twists on itself, causing severe pain and requiring immediate medical attention—or infection.
Stage 4: Fertilization, Embryo Culture, and Embryo Selection
One to four hours after retrieval, the eggs are introduced to the sperm. Fertilization is carried out using conventional insemination or ICSI if there are indications of male factor infertility. Fertilization evaluation is conducted 16–18 hours later to confirm the formation of two pronuclei—a sign of successful fertilization, visible as two round dots inside the egg, each carrying genetic material from the sperm and the egg.
The successfully fertilized embryos are cultured in a specialized medium. Most laboratories recommend culturing up to the blastocyst stage (the embryo development stage around day 5, ready for implantation into the uterus). This extended culture allows for natural selection of embryos with the highest developmental potential, while also reducing the risk of multiple pregnancies through the application of elective single embryo transfer (eSET).
Based on the latest clinical guidelines from ESHRE (European Society of Human Reproduction and Embryology) and ASRM, the decision to transfer two embryos instead of one should not be based on a history of previous IVF failures or the duration of infertility. For frozen embryos that have undergone vitrification (an ultra-rapid embryo freezing method to prevent the formation of ice crystals that damage cells), single embryo transfer is highly recommended. Cryopreservation (storing embryos at very low temperatures for future use) is performed with one embryo per storage device to consistently support single embryo transfer practices.
Stage 5: Embryo Transfer and Luteal Phase Support Monitoring
The embryo transfer procedure does not require anesthesia as it causes very minimal discomfort. The doctor uses a soft catheter inserted through the cervix (the lower part of the uterus connecting the uterus to the vagina) into the uterine cavity under abdominal ultrasound guidance.
To ensure the uterus is prepared to receive the embryo, the patient is given luteal phase support (the administration of progesterone and estrogen hormones post-transfer to prepare and maintain the uterine lining so the embryo can implant and develop). This therapy is administered via the oral route, vaginal suppositories, or injections, and is continued until 10–12 weeks of gestation if the result is positive.
Pregnancy evaluation is conducted via a blood hCG test 9–14 days post-transfer, followed by an obstetric ultrasound to ensure the gestational sac is located within the uterine cavity (the space inside the uterus where a healthy pregnancy should develop).
Summary of IVF Stages
Clinical Stages of IVF
Estimated Duration
Primary Intervention / Medical Therapy
Clinical Objective
Estrogen Priming
1–3 Weeks
Oral/patch estrogen or oral contraceptives
Synchronizing follicular condition in the ovaries prior to stimulation
Ovarian Stimulation
8–12 Days
Gonadotropin injections (FSH & LH) + GnRH antagonist/agonist
Stimulating multiple mature follicles; preventing premature ovulation
Egg Retrieval
1 Day (34–36 hours post-trigger shot)
Transvaginal aspiration with a specialized needle under sedation
Collecting mature eggs for laboratory fertilization
Embryo Culture
3–7 Days
Laboratory incubation in specialized culture medium
Selecting the best embryos up to the blastocyst stage
Embryo Transfer
1 Day
Soft catheter via ultrasound guidance + luteal phase support
Implanting the embryo into the uterus; hormonal support for pregnancy
Next Steps
If you are preparing to begin an IVF program, knowing each clinical stage in a structured manner will help you and your partner navigate this process more calmly and optimally.
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References
• American Urological Association and American Society for Reproductive Medicine. Diagnosis and Treatment of Infertility in Men.
• European Association of Urology. Sexual and Reproductive Health Guidelines: Male Infertility.
• IVF Process Day by Day – In Vitro Fertilization Steps. CCRM.
• ESHRE guideline: number of embryos to transfer during IVF/ICSI.
Disclaimer: This information is for educational purposes and does not replace a physician’s evaluation. Diagnostic and therapeutic decisions should be tailored to the examination results of you and your partner.
