In Vitro Fertilization (IVF) is a medical procedure classified as an Assisted Reproductive Technology (ART), where the fertilization of an egg by sperm occurs outside the body in a laboratory setting. This process is often chosen by individuals or couples facing difficulties with natural conception due to various factors, including male-factor infertility, blocked fallopian tubes, or unexplained infertility. A typical IVF cycle is a sequence of steps that begins with hormonal preparation and concludes with a pregnancy test. The cycle generally spans four to six weeks from the start of medication to the final outcome, guided by a medical team focused on maximizing the chances for a successful, healthy pregnancy.
Initial Preparation and Ovarian Stimulation
The IVF cycle begins with an initial preparation phase, which includes various screening tests and baseline assessments. This involves bloodwork to check hormone levels, such as Anti-Müllerian Hormone (AMH), Follicle-Stimulating Hormone (FSH), and Estradiol, alongside a transvaginal ultrasound to evaluate the uterus and ovaries. These preliminary steps help the clinician tailor the subsequent medication protocol to the individual patient.
The core of this phase is controlled ovarian hyperstimulation (COH), designed to encourage the ovaries to produce multiple mature eggs in a single cycle, rather than the single egg typically released naturally. This process usually involves 10 to 14 days of self-administered daily hormone injections, which contain synthetic versions of gonadotropins like FSH and Luteinizing Hormone (LH). These medications stimulate the growth of multiple fluid-filled sacs, called follicles.
Frequent monitoring is necessary during this stimulation period to track the development of the follicles. Patients visit the clinic every few days for transvaginal ultrasounds, which measure the size and number of growing follicles. Concurrently, blood tests are performed to measure estrogen levels, allowing the medical team to precisely adjust the medication dosages.
Once the lead follicles reach an optimal size, typically between 17 and 18 millimeters, the stimulation phase is concluded with a single injection known as the “trigger shot.” This shot, often containing human Chorionic Gonadotropin (hCG) or a GnRH agonist, mimics the body’s natural LH surge, prompting the final maturation of the eggs. The timing of this injection is critical, as egg retrieval must be precisely scheduled for 34 to 36 hours later.
Egg Retrieval and Fertilization Procedures
The egg retrieval is a minor surgical procedure performed in the clinic’s operating suite, typically under light intravenous (IV) sedation. The clinician uses a transvaginal ultrasound probe to visualize the ovaries and guides a thin needle through the vaginal wall into each mature follicle. Gentle suction is applied to aspirate the fluid from the follicles, which is immediately passed to the embryology laboratory for analysis.
In the lab, embryologists examine the follicular fluid under a microscope to identify the eggs, which are then assessed for maturity. Simultaneously, the sperm sample—either from a partner or a donor—is prepared, selecting the most motile and morphologically sound sperm. The retrieved eggs and prepared sperm are then moved to the fertilization stage.
Fertilization can occur via one of two primary methods. Conventional IVF involves placing the eggs and a concentration of sperm together in a culture dish, allowing the sperm to naturally penetrate the egg. The alternative is Intracytoplasmic Sperm Injection (ICSI), where an embryologist uses a specialized needle to physically inject a single, selected sperm directly into the center of each mature egg. ICSI is frequently used in cases of male-factor infertility, such as low sperm count or poor motility, or when previous IVF cycles have resulted in low fertilization rates.
Embryo Culture, Grading, and Transfer
Following insemination, the now-fertilized eggs, called zygotes, are placed in a specialized incubator to begin the Embryo Culture process. For the next three to seven days, the embryos are maintained in a carefully controlled environment, mimicking the conditions of the fallopian tube and uterus. Embryologists monitor their development closely, checking for signs of cell division and progression.
The embryos are regularly subjected to Embryo Grading, an evaluation process that assesses their quality and developmental potential. Early-stage embryos (Day 3) are graded based on the number of cells and the degree of cell symmetry and fragmentation. The most viable embryos are cultured further until they reach the blastocyst stage, which occurs five to seven days after retrieval.
Blastocysts are graded using a complex system that evaluates three key features: the degree of expansion; the quality of the inner cell mass (ICM), which will become the fetus; and the quality of the trophectoderm (TE), which will form the placenta. Embryos deemed of the highest quality are selected for immediate transfer. Remaining viable embryos are preserved through cryopreservation (freezing) for potential future use. This practice allows for subsequent frozen embryo transfer (FET) cycles without the need for another full ovarian stimulation and retrieval.
The Embryo Transfer is the final procedural step, performed without anesthesia. The selected embryo is loaded into a thin, flexible catheter. The clinician guides the catheter through the cervix and into the uterus, often using abdominal ultrasound imaging for precise placement. The embryo is gently expelled into the uterine cavity, where it is hoped it will implant into the prepared uterine lining.
The Final Phase and Outcome
Immediately following the transfer, the patient enters the “two-week wait,” or the luteal phase, a period of approximately 10 to 14 days before a pregnancy can be reliably confirmed. During this time, patients are often prescribed progesterone medication, administered via a vaginal insert, injection, or oral pill. This supplemental progesterone helps to support and maintain the uterine lining, creating an optimal environment for the embryo to implant and continue its development.
This waiting period is characterized by the embryo’s attempt to implant, which typically occurs within the first five days after transfer. If implantation is successful, the developing embryo begins to produce the hormone human Chorionic Gonadotropin (hCG). The cycle’s outcome is determined by a quantitative blood test, known as the beta HCG test, performed toward the end of the two-week wait.
A positive result indicates that detectable levels of HCG are present, confirming a pregnancy. If the initial HCG level is low or equivocal, the test is repeated 48 to 72 hours later to ensure the hormone is doubling appropriately. Conversely, a negative test result indicates that implantation did not occur. The medical team will then discuss the next steps, which may involve planning a subsequent cycle using cryopreserved embryos or beginning a new fresh cycle.