IVF Step by Step: How an IVF Cycle Works

Why is IVF done outside the body?

In natural conception, fertilization happens inside the fallopian tube. IVF moves that process into a laboratory so clinicians can:

• Retrieve multiple eggs in a single cycle (increasing the number of chances)
• Select the best-quality sperm for fertilization
• Monitor embryo development directly
• Test embryos for chromosomal abnormalities before transfer (preimplantation genetic testing, or PGT)
• Freeze surplus embryos for future attempts
• Transfer embryos in a carefully prepared uterine environment

This level of control makes IVF more effective per cycle than IUI for many diagnoses, particularly as age increases and egg quality becomes more variable 1Ref 1Practice Committee of the American Society for Reproductive Medicine (2020).Evidence-based treatments for couples with unexplained infertility: a guideline.IVF as a higher-efficacy per-cycle treatment compared to IUI; rationale for moving to IVF for unexplained infertility after failed IUI cycles. The tradeoff is a more intensive process with greater physical, emotional, and financial investment.

Step 1: Ovarian stimulation (about 8 to 14 days)

The natural menstrual cycle typically produces one mature egg. To maximize the number of eggs retrieved in one cycle, IVF uses injectable hormonal medications (gonadotropins — FSH and/or LH) to stimulate the ovaries to develop multiple follicles simultaneously.

During this phase: - You inject medications at home (usually in the abdomen) every day, sometimes twice a day - You return to the clinic every few days for transvaginal ultrasound to monitor follicle development and blood tests (estrogen levels) - The doses may be adjusted based on how your ovaries respond - When the leading follicles reach the appropriate size (usually 17–20 mm), a "trigger shot" (hCG or a GnRH agonist) is administered to complete egg maturation - Egg retrieval is scheduled precisely 34–36 hours after the trigger

A medication to prevent premature ovulation (GnRH agonist or antagonist protocol) is also part of most protocols. The specific protocol design varies by clinic and individual response profile.

Step 2: Egg retrieval (a brief procedure under sedation)

Egg retrieval is done as an outpatient procedure, typically under light sedation (you are comfortable and unaware but not under general anesthesia).

Using transvaginal ultrasound guidance, a thin needle is passed through the vaginal wall into each mature follicle to aspirate the fluid — and hopefully the egg — from each one. The procedure takes approximately 20–30 minutes. You will need someone to drive you home and should rest that day.

Afterward: - Cramping and mild bloating are expected for a day or two - Spotting is normal - Your clinic will call you the next morning with a fertilization report: how many eggs were retrieved, how many were mature, and how many fertilized

The number of eggs retrieved varies widely depending on age and ovarian reserve — it is one of the most variable parts of the process. Ovarian hyperstimulation syndrome (OHSS), a serious but uncommon complication of stimulation, is monitored for during and after this phase 3Ref 3Practice Committee of the Society for Reproductive Endocrinology and Infertility; Quality Assurance Committee of SART; Practice Committee of ASRM (2022).Multiple gestation associated with infertility therapy: a committee opinion.Single embryo transfer recommendation to minimize multiple pregnancy risk; OHSS monitoring during stimulation; multiple gestation as an adverse outcome to prevent.

Step 3: Fertilization and embryo development (5 to 7 days in the lab)

In the laboratory, each mature egg is fertilized using one of two methods:

• Conventional insemination: the egg and a concentration of sperm are placed together in a dish and fertilization occurs naturally
• ICSI (intracytoplasmic sperm injection): a single sperm is injected directly into the egg using a microscopic needle. Used when sperm parameters are limited or when prior fertilization was poor.

The fertilized eggs (now called embryos) are cultured in the laboratory for 5–7 days. Most clinics allow embryos to develop to the blastocyst stage (day 5–6) — a more advanced stage that correlates better with implantation potential.

The embryologist monitors development daily. Not all fertilized eggs become blastocysts — attrition between retrieval and blastocyst is expected and reflects normal embryo biology.

Preimplantation genetic testing (PGT-A): if genetic testing is planned, a small biopsy of cells is taken from the blastocyst before freezing. Results take 1–2 weeks, so a fresh transfer is usually not done in a PGT cycle. A 2024 ASRM opinion noted that PGT-A has not been demonstrated to improve outcomes for all IVF patients as routine screening — discuss with your physician whether it is appropriate for your situation 2Ref 2Practice Committees of the American Society for Reproductive Medicine and the Society for Assisted Reproductive Technology (2024).The use of preimplantation genetic testing for aneuploidy: a committee opinion.PGT-A has not been demonstrated to improve outcomes for all IVF patients as routine screening; decision for genetic testing should be individualized; euploid SET recommended.

Step 4: Embryo transfer

Embryo transfer is simpler than egg retrieval — it does not require sedation and takes only a few minutes.

A thin, flexible catheter is guided through the cervix into the uterine cavity under ultrasound guidance, and the embryo(s) are gently released. You will likely be asked to rest briefly after, though evidence does not support prolonged bed rest improving outcomes.

Fresh vs. frozen transfer: - *Fresh transfer:* done a few days after retrieval in the same cycle — less common now in many clinics, as frozen transfers have become standard in many situations - *Frozen embryo transfer (FET):* the embryo is frozen, and transfer is done in a subsequent cycle with a carefully prepared uterine lining (estrogen followed by progesterone). FET allows time for PGT results, allows the body to recover from stimulation, and is now the predominant approach in many clinics

The number of embryos to transfer is a critical conversation with your reproductive endocrinologist. To minimize multiple pregnancy risk, most clinics now recommend single embryo transfer (SET) for most patients, particularly those with good-prognosis embryos 1Ref 1Practice Committee of the American Society for Reproductive Medicine (2020).Evidence-based treatments for couples with unexplained infertility: a guideline.IVF as a higher-efficacy per-cycle treatment compared to IUI; rationale for moving to IVF for unexplained infertility after failed IUI cycles3Ref 3Practice Committee of the Society for Reproductive Endocrinology and Infertility; Quality Assurance Committee of SART; Practice Committee of ASRM (2022).Multiple gestation associated with infertility therapy: a committee opinion.Single embryo transfer recommendation to minimize multiple pregnancy risk; OHSS monitoring during stimulation; multiple gestation as an adverse outcome to prevent.

Step 5: The two-week wait and pregnancy test

After transfer, a blood pregnancy test (measuring hCG) is typically done 9–12 days later. This two-week wait ("the 2WW") is emotionally demanding for most people — the uncertainty combined with the investment in the cycle is significant.

Progesterone supplementation (vaginal suppositories, injections, or oral tablets) is standard after transfer to support the uterine lining.

A positive blood hCG that rises appropriately leads to an early viability ultrasound at approximately 6–7 weeks. If the cycle does not result in pregnancy, a review appointment is typically scheduled to discuss what was learned and whether adjustments are needed for a subsequent cycle.

Gale can help you prepare thoughtful questions for a reproductive endocrinologist consultation before starting an IVF cycle.