In vitro fertilization works by combining eggs and sperm in a laboratory, then transferring the resulting embryo into the uterus. A full IVF cycle typically takes four to six weeks from the start of medication to embryo transfer, though many people now freeze their embryos and transfer them in a later cycle. The process involves several distinct phases: preparation and testing, ovarian stimulation, egg retrieval, fertilization, embryo culture, and transfer.
Pre-Treatment Testing
Before an IVF cycle begins, both partners undergo diagnostic testing to help the fertility team design a treatment plan. For the person providing eggs, this includes a transvaginal ultrasound to examine the uterus and ovaries and count the small fluid-filled sacs (antral follicles) visible on each ovary. Blood tests drawn early in the menstrual cycle measure key hormones, most importantly anti-Müllerian hormone (AMH), which estimates how many eggs the ovaries are likely to produce in response to stimulation. Together, the follicle count and AMH level give the clearest picture of ovarian reserve.
For the sperm provider, a semen analysis evaluates sperm concentration, movement, and shape. These results determine whether standard fertilization or a more targeted approach will be used later in the process. Additional screening may include infectious disease panels, uterine imaging, and genetic carrier testing depending on medical history.
Ovarian Stimulation
In a natural cycle, the ovaries release one egg per month. IVF aims to produce multiple mature eggs at once, which improves the odds of creating viable embryos. To do this, you take injectable hormones, primarily synthetic versions of the same hormones your brain naturally sends to your ovaries: follicle-stimulating hormone (FSH) and sometimes luteinizing hormone (LH). These medications push multiple follicles to grow simultaneously rather than allowing a single dominant follicle to take over.
At the same time, you take a second medication to prevent your body from ovulating too early. These drugs block the natural hormonal surge that would release the eggs before they can be collected. The stimulation phase lasts 8 to 12 days. During that window, you visit the clinic four to six times for short ultrasound and blood draw appointments, each about 15 to 20 minutes, so the team can track follicle growth and adjust your medication doses.
Some protocols include a “priming” phase of one to three weeks before stimulation begins, using birth control pills or other hormones to synchronize follicle development. Not everyone needs this step.
The Trigger Shot and Egg Retrieval
Once the follicles reach the right size, you receive a precisely timed injection called the trigger shot, which initiates the final maturation of the eggs. Ovulation would naturally occur about 37 to 38 hours later, so the retrieval is scheduled just before that window, typically 35 to 36 hours after the injection.
Egg retrieval is a short outpatient procedure done under sedation. Using ultrasound guidance, a thin needle passes through the vaginal wall into each ovary, and the fluid inside each follicle is aspirated along with the egg it contains. The procedure takes roughly 15 to 30 minutes. Most people experience cramping and bloating afterward and can return to normal activity within a day or two.
Fertilization in the Lab
Once the eggs are collected, they are fertilized using one of two methods. In conventional IVF, each egg is placed in a dish with a concentrated sample of sperm and left overnight. The sperm compete to penetrate the egg naturally, much as they would in the body.
The alternative is intracytoplasmic sperm injection, or ICSI. An embryologist selects a single sperm under a microscope and injects it directly into the egg. ICSI is typically used when sperm counts or motility are low, but many clinics now use it routinely. Before injection, the protective layer of cells surrounding the egg is removed, which also reduces the risk of contamination during later genetic testing.
By the morning after retrieval, roughly 18 to 24 hours after eggs and sperm are combined, the lab can confirm how many eggs have fertilized. Not every mature egg will fertilize successfully, and the number that do is the starting pool for the next phase.
Embryo Development: Day 3 vs. Day 5
Fertilized eggs are cultured in the lab under carefully controlled conditions. Over the next several days, embryologists monitor cell division and overall quality. On day three, a healthy embryo has divided into roughly eight cells. By day five, it has developed into a blastocyst, a more complex structure of around 100 cells with two distinct parts: an inner cell mass that will become the fetus and an outer layer that will become the placenta.
Most clinics now culture embryos to the blastocyst stage rather than transferring at day three. There are several reasons for this. In a natural pregnancy, an embryo doesn’t reach the uterus until the blastocyst stage, so the timing aligns better. Waiting until day five also acts as a natural selection process. Embryos that can’t sustain their own development tend to stop growing, which means the ones that survive are statistically more likely to implant. Blastocyst transfers have been shown to increase pregnancy rates by 3 to 10% and live birth rates by 3 to 13% compared to day-three transfers. Transferring at the blastocyst stage also makes single-embryo transfer more practical, reducing the chance of twins or triplets.
Embryos are graded at each stage based on cell number, symmetry, and fragmentation. On day five, grading considers the size of the fluid-filled cavity, the inner cell mass, and the outer cell layer. Top-quality embryos have the best statistical chance of implantation, but lower-graded embryos can and do produce healthy pregnancies.
Genetic Testing Before Transfer
Many patients opt for preimplantation genetic testing, which involves removing a few cells from the outer layer of a day-five or day-six blastocyst and analyzing them. The most common form, PGT-A, screens for the correct number of chromosomes. Embryos with extra or missing chromosomes (aneuploidy) are the leading cause of failed implantation and early miscarriage. Selecting chromosomally normal embryos for transfer improves implantation rates and reduces miscarriage risk, with the greatest benefit seen in patients over 35.
A second type, PGT-M, tests for specific inherited genetic conditions like cystic fibrosis or sickle cell disease when one or both parents are known carriers. Genetic testing adds time to the process because embryos are frozen while awaiting results, which typically take one to two weeks.
Fresh vs. Frozen Embryo Transfer
A fresh transfer happens within the same cycle as egg retrieval, typically on day five after fertilization. A frozen transfer, or FET, means the embryos are cryopreserved and transferred in a separate, later cycle. The trend in fertility medicine has shifted strongly toward freezing, and the data supports it.
Frozen transfers consistently produce better outcomes. In one large study, clinical pregnancy rates were 47.5% with frozen embryos compared to 35.5% with fresh. Live birth rates were also significantly higher: 38.8% in the frozen group versus 15.7% in the fresh group. Frozen transfers also carried lower rates of multiple pregnancies, preterm delivery, low birth weight, and first-trimester miscarriage.
The likely explanation is timing. After ovarian stimulation, the uterine lining may not be optimally synchronized with the embryo. A frozen transfer allows the lining to develop naturally or with gentle hormonal support in a cycle unaffected by stimulation drugs, creating better conditions for implantation. If you undergo genetic testing, a frozen transfer is the default since results take time.
The Transfer Procedure
Embryo transfer itself is one of the simplest parts of the process. It does not require sedation. A thin, flexible catheter is guided through the cervix into the uterus using ultrasound, and the embryo is deposited. The entire procedure takes a few minutes. Most clinics now transfer a single embryo to minimize the risk of multiples, particularly when using a genetically tested blastocyst.
After the transfer, you typically wait about 10 to 14 days before taking a blood pregnancy test. This waiting period is often described as the most emotionally difficult part of the cycle.
Success Rates by Age
According to 2022 CDC data, the average live birth rate per IVF cycle across all ages is 37.5%. Age is the single strongest predictor of success, primarily because egg quality declines over time.
- Under 35: 36% live birth rate per cycle
- 35 to 37: 23.5%
- 38 to 40: 20.6%
- 41 to 42: 9.7%
- Over 42: 10.3%
These are per-cycle averages, meaning cumulative success rates over multiple cycles are higher. Many people require more than one cycle to achieve a live birth. Using donor eggs largely eliminates the age-related decline, which is why success rates for patients over 42 using their own eggs differ dramatically from those using younger donors.
Costs
The U.S. Department of Health and Human Services estimates a single IVF cycle costs between $15,000 and $20,000, including medications and lab fees. Cycles involving donor eggs can exceed $30,000. These figures can vary widely by clinic and region. Add-ons like genetic testing, embryo freezing, and storage fees increase the total. Insurance coverage for IVF varies significantly by state and employer, with some states mandating partial or full coverage and many offering none at all.
Risks and Side Effects
The most common side effects during stimulation are bloating, mood changes, headaches, and injection-site soreness. The most significant medical risk is ovarian hyperstimulation syndrome (OHSS), where the ovaries overreact to stimulation hormones. Mild to moderate OHSS causes abdominal pain, bloating, nausea, and slight weight gain. It occurs in fewer than 5% of IVF patients today, down from about 10% in earlier years, thanks to improved monitoring and newer trigger shot options. Severe OHSS, which can cause difficulty breathing, blood clots, and significant fluid retention, happens in less than 1% of cases and requires medical attention.
After egg retrieval, cramping and spotting are normal. The risk of infection or bleeding from the procedure is low. The emotional toll of IVF, including the uncertainty, hormonal fluctuations, and financial pressure, is real and worth preparing for, even though it doesn’t appear on a medical risk list.