In vitro fertilization (IVF) is a process involving multiple sequential steps. The question of when an IVF cycle officially begins is complex because the process is not a single event but a collection of coordinated phases. The start is determined by a combination of preparatory requirements, a patient’s natural menstrual cycle, and the specific medical protocol chosen. Understanding the chronological phases, from initial testing to the start of hormonal medications, clarifies the timeline of a treatment cycle.
Required Preparatory Steps
Before any hormonal medications can be prescribed to stimulate the ovaries, a patient and their partner must complete a series of administrative and diagnostic hurdles. This preparatory phase ensures the safety and readiness of both the individuals and the clinic for the intensive treatment ahead. Necessary medical screenings include blood tests for infectious diseases, such as HIV, Hepatitis B and C, and syphilis, to mitigate risks to the developing fetus and the laboratory staff.
A detailed assessment of the uterus is also completed, often through a saline sonogram or hysteroscopy, to check for structural issues like polyps, fibroids, or scar tissue that could interfere with embryo implantation. Ovarian reserve testing, typically involving blood tests for Follicle-Stimulating Hormone (FSH) and Anti-Müllerian Hormone (AMH), combined with an antral follicle count ultrasound, gives the medical team a baseline measure of egg quantity and quality. Only once all diagnostic results are finalized, consent forms are signed, and a personalized treatment plan is created, can the actual medical cycle be scheduled to begin.
Defining Cycle Day One
The medical start of the active treatment phase is most often triggered by a natural physiological event: the onset of a full menstrual period. This specific day is designated as Cycle Day One (CD1) and is the chronological reference point for the entire stimulation cycle. Spotting does not count as CD1; the definition requires the first day of full, unmistakable menstrual flow.
Following CD1, the patient attends a baseline appointment, typically on CD2 or CD3, for a transvaginal ultrasound and blood work. The ultrasound confirms that the ovaries are “quiet,” meaning there are no residual large cysts from the previous cycle, and the uterine lining is thin. Blood tests check hormone levels, particularly estrogen and progesterone, to ensure they are at a low baseline state, which confirms the body is ready to begin external hormonal stimulation. If these baseline results are acceptable, the medical team gives the instruction to start the stimulating injections, initiating the ovarian stimulation phase of IVF.
Hormonal Synchronization Before Stimulation
While the period marks the natural start of a cycle, many IVF protocols involve a phase of hormonal synchronization that takes place before stimulation injections begin. This is often achieved using oral contraceptive pills (OCPs) or GnRH agonists like Lupron. The primary purpose of this pre-treatment is to achieve a uniform cohort of small follicles and prevent premature ovulation, known as cycle down-regulation or suppression.
Using OCPs can also serve a logistical purpose, allowing the clinic and the patient to schedule the egg retrieval procedure for a specific time, avoiding weekend monitoring. In some cases, GnRH agonists are started in the middle of the previous cycle to suppress the pituitary gland’s natural hormone production, ensuring that the body’s hormones do not interfere with the prescribed stimulation medications. This synchronization phase adds time to the overall process but provides the medical team with greater control over the subsequent stimulation phase.
Common Timing Protocols
The time between starting preparatory medications and beginning the ovarian stimulation injections varies depending on the specific protocol chosen. The two most common approaches are the Antagonist protocol and the Agonist or Long protocol, which differ in their suppression strategy and duration. The Antagonist protocol is generally shorter, with stimulation injections often starting directly after the baseline appointment on CD2 or CD3.
In this protocol, a second medication, a GnRH antagonist, is introduced around the fifth or sixth day of stimulation to prevent the luteinizing hormone (LH) surge that causes premature ovulation. Conversely, the Agonist/Long protocol involves a longer pre-stimulation phase, often requiring the use of a GnRH agonist to fully suppress the pituitary gland for approximately two to three weeks before the stimulation injections are introduced. This difference in the initial suppression phase dictates whether the patient begins stimulating medications immediately after their period starts or after a three-week period of down-regulation.