In Vitro Fertilization (IVF) is a medical process where an egg is fertilized by sperm outside the body before the resulting embryo is transferred to the uterus. A central step in this treatment is controlled ovarian stimulation, often informally called “stims.” This phase involves daily injections of hormone medications to encourage the ovaries to develop multiple mature eggs, rather than the single egg typically released in a natural menstrual cycle. The precise timing of when these injectable medications begin is highly individualized, depending on the patient’s specific protocol and their body’s readiness.
Essential Pre-Cycle Preparations
Before the first stimulation injection, preparatory steps are necessary to optimize the ovarian environment. Many patients start by taking oral contraceptive pills or using estrogen patches for a few weeks to regulate their natural cycle. This practice helps synchronize the growth of small follicles and allows the clinic to schedule the procedure start date predictably by placing the ovaries into a quiet, uniform state.
This quiet state is confirmed through a baseline assessment, typically occurring on Cycle Day 2 or 3 once menstrual bleeding has begun. The assessment involves a transvaginal ultrasound and a blood test to check specific hormone levels. The ultrasound confirms the absence of large ovarian cysts or residual follicles that could interfere with the development of the new eggs. Simultaneously, the blood work confirms low hormone levels, indicating the pituitary gland is suppressed and the ovaries are dormant.
Varying Protocols for Starting Stimulation
The timing of the first stimulation injection is dictated by the specific protocol chosen.
Antagonist Protocol
The most common approach is the Antagonist Protocol, where stimulation begins early in the menstrual cycle, typically on Cycle Day 2 or 3. This follicular phase start leverages the natural window of follicle recruitment. Stimulation medications, containing Follicle-Stimulating Hormone (FSH), are administered for about 8 to 14 days.
A second medication, a GnRH antagonist, is introduced later, usually around day five or six of stimulation. This drug prevents an unplanned surge of Luteinizing Hormone (LH) from the brain, which would cause premature egg release before retrieval. This protocol is popular because it is shorter and involves less pre-treatment medication.
Agonist (Long) Protocol
The Agonist, or Long Protocol, requires two to three weeks of preparation before stimulation begins. This protocol involves starting a GnRH agonist medication in the luteal phase, about a week before the expected period of the cycle preceding the stimulation cycle. The purpose of this medication is to temporarily suppress the pituitary gland, a process called down-regulation, which ensures complete control over the ovaries.
Once down-regulation is confirmed, the daily stimulation injections are added to the regimen. This approach ensures maximum ovarian suppression, preventing a spontaneous LH surge, but it requires a longer period of medication use.
Luteal or Random Start Protocol
A third timing strategy is the Luteal or Random Start Protocol, often used for urgent fertility preservation or “double stimulation” in a single cycle. In this protocol, stimulation can be initiated at virtually any point in the cycle, including the luteal phase, provided baseline criteria are met. Since the endometrium is not optimized for a fresh transfer when stimulating later in the cycle, this approach necessitates freezing all resulting embryos or eggs for a later transfer.
Determining the Exact Start Day
Regardless of the chosen protocol, the final decision to start injectable stimulation medications rests on immediate biological confirmation from the baseline blood test and ultrasound. Hormone levels must meet specific criteria to ensure the ovaries are properly suppressed and ready to respond predictably.
The Estradiol (E2) hormone level must be low, typically falling below 50 to 80 picograms per milliliter (pg/mL). An elevated Estradiol level suggests an active follicle or functional cyst, necessitating a cycle delay. The progesterone level must also be low to confirm that no recent ovulation has occurred.
The accompanying ultrasound must confirm “ovarian silence,” meaning there are no large follicles (over three centimeters) or cysts present on the ovaries. The thinness of the uterine lining is also checked to confirm the start of the follicular phase. Only when these baseline criteria are met does the physician instruct the patient to begin the daily stimulation injections.