In vitro fertilization (IVF) involves collecting eggs from the ovaries, fertilizing them with sperm in a laboratory, then transferring an embryo back into the uterus. A fresh cycle typically takes four to six weeks from the start of medication to embryo transfer, with a pregnancy blood test nine to 14 days after that. Each stage builds on the one before it, and understanding the full sequence helps you know what to expect at every step.
Ovarian Stimulation
A natural menstrual cycle produces one mature egg. IVF needs more than one to work with, so the process begins with hormone injections that push the ovaries to develop multiple eggs simultaneously. These medications contain follicle-stimulating hormone (FSH), sometimes combined with luteinizing hormone (LH), and are self-injected daily for roughly 8 to 14 days.
During this phase, you’ll visit the clinic every two to three days for monitoring. A transvaginal ultrasound tracks the number and size of developing follicles (the fluid-filled sacs that hold eggs), and some clinics also draw blood to measure estrogen levels. The goal is to determine exactly when the follicles are mature enough for retrieval. When they reach the right size, you’ll take a final “trigger shot” of human chorionic gonadotropin (hCG) or a similar hormone that prompts the eggs to complete their maturation. Egg retrieval is scheduled about 36 hours later.
Egg Retrieval
Retrieval is a short procedure, typically 15 to 30 minutes, done in your fertility clinic. You’ll receive IV sedation, so you’re not fully under general anesthesia but you shouldn’t feel significant discomfort. Using ultrasound guidance, the doctor passes a thin needle through the vaginal wall into each ovary and gently suctions the fluid from each follicle, collecting the eggs.
Most people go home within an hour or two afterward. Cramping and bloating are common for a day or so. Your partner or a sperm donor provides a semen sample the same day, unless frozen sperm is being used.
Fertilization in the Lab
Once eggs are retrieved, they’re taken to the embryology lab where fertilization happens one of two ways. In conventional IVF, each egg is placed in a dish with roughly two to five million prepared sperm, and fertilization occurs naturally overnight. In ICSI (intracytoplasmic sperm injection), an embryologist selects a single sperm and injects it directly into the egg.
ICSI is typically used when sperm count or motility is low, or when previous IVF cycles had poor fertilization. For couples without a clear male-factor issue, conventional insemination and ICSI produce similar results. The embryology team checks the eggs the following morning to confirm which ones fertilized successfully.
Embryo Development and Grading
Fertilized eggs are cultured in the lab for three to five days. Embryologists evaluate them at two key checkpoints.
On day three, the embryo is at the “cleavage stage,” actively dividing but still the same size as the original egg. An ideal day-three embryo has about eight cells of fairly uniform size, with less than 20% fragmentation (tiny bits of cellular material that break off during division). Embryos with fewer cells can still lead to healthy pregnancies, but eight or more cells is the strongest indicator of potential.
By day five, the embryo has reached the blastocyst stage. It now has two distinct cell groups: an inner cell mass that will become the fetus, and an outer layer called the trophectoderm that will form the placenta. A fluid-filled cavity expands inside the embryo. Blastocysts are graded on a scale of 1 to 6 based on how much this cavity has expanded, plus separate letter grades for the quality of the inner cell mass and outer layer. A grade of 4AA, for example, would indicate a well-expanded blastocyst with high-quality cells in both regions.
Most clinics now culture embryos to the blastocyst stage before transfer, since reaching day five is itself a sign of viability.
Optional Genetic Testing
Before transfer, you may choose to have embryos biopsied for genetic testing. A few cells are removed from the outer layer of the blastocyst (the part destined to become placenta, not the fetus) and sent to a genetics lab.
The two most common types of testing are PGT-A and PGT-M. PGT-A screens for aneuploidy, meaning embryos that have too many or too few chromosomes. Chromosomal abnormalities are the leading cause of failed implantation and early miscarriage, and they become more common with age. PGT-M tests for a specific inherited condition, like cystic fibrosis or sickle cell disease, when one or both parents are known carriers. Both types of testing can be run simultaneously from the same biopsy.
Genetic testing adds one to two weeks to the timeline because embryos are frozen while awaiting results. Transfer then happens in a subsequent cycle.
Embryo Transfer
Transfer is the simplest procedure in the entire process. It takes only a few minutes and usually requires no sedation. The doctor loads the selected embryo into a thin, flexible catheter and threads it through the cervix into the uterus, using abdominal ultrasound to guide placement. You’ll be asked to have a comfortably full bladder, which helps with ultrasound visibility.
Current guidelines from the American Society for Reproductive Medicine strongly recommend transferring a single embryo for most patients. Transferring one genetically tested (euploid) embryo produces pregnancy rates similar to transferring two untested embryos, while dramatically reducing the chance of twins. For patients under 38 with a favorable prognosis, single embryo transfer is the standard. The recommended upper limit increases slightly with age and depending on embryo quality, but the overall trend in reproductive medicine has been firmly toward one embryo at a time.
Any high-quality embryos not transferred can be frozen (vitrified) for future use.
The Two-Week Wait and Pregnancy Test
After transfer, you’ll typically start progesterone supplementation, delivered as vaginal suppositories, injections, or both, to support the uterine lining during the implantation window. There’s no specific activity restriction required, despite the common instinct to stay in bed.
Nine to 14 days after transfer, you’ll return to the clinic for a blood test measuring hCG, the hormone produced by an implanting embryo. A home pregnancy test can sometimes detect hCG in this window too, but blood testing gives a precise measurement and is repeated two to three days later to confirm the hormone level is rising appropriately. A positive, rising hCG leads to an ultrasound about two weeks later to confirm a heartbeat.
Risks to Be Aware Of
The most significant medical risk specific to IVF is ovarian hyperstimulation syndrome (OHSS), where the ovaries overreact to the stimulation hormones and become swollen and painful. Mild OHSS, involving bloating, nausea, and abdominal discomfort, is relatively common and resolves on its own. Moderate to severe OHSS is less frequent but more serious, causing rapid weight gain (a kilogram or more in 24 hours), severe abdominal pain, difficulty breathing, and fluid accumulation in the abdomen. In rare critical cases, it can lead to blood clots, kidney problems, or respiratory distress.
Your clinic monitors for OHSS risk throughout stimulation. If your ovaries are responding too aggressively, your doctor can adjust medication doses, change the type of trigger shot used, or recommend freezing all embryos and delaying transfer to a later cycle, which significantly reduces the severity of symptoms.
Other risks include the standard minor risks of any procedure involving sedation and a needle, such as infection or bleeding during retrieval, though these are uncommon. Multiple pregnancies carry their own set of health risks for both parent and babies, which is the primary reason single embryo transfer has become the default recommendation.
What Affects Success Rates
Age is the single largest factor influencing IVF outcomes. Egg quality declines with age, and so do live birth rates per cycle. For patients under 35 using their own eggs, cumulative live birth rates (including fresh and frozen transfers from one egg retrieval) are substantially higher than for patients over 40. The CDC publishes clinic-level success rate data annually, with the most recent report covering 2022 cycles. These numbers can be filtered by age group and whether the patient had prior IVF attempts.
Beyond age, success depends on the cause of infertility, the number of eggs retrieved, embryo quality, uterine health, and lifestyle factors like smoking and body weight. Choosing a clinic with high single-embryo-transfer rates is worth paying attention to, since clinics that transfer one embryo in patients under 38 have been shown to maintain strong live birth rates while avoiding the complications of twins and higher-order multiples.