In Vitro Fertilization (IVF) involves a careful, multi-step process, and one of the most significant phases is Ovarian Stimulation, often referred to as “stims.” This phase uses injectable hormone medications to encourage the ovaries to produce multiple mature eggs in a single treatment cycle. While the body typically matures only one egg per cycle, maximizing the number of eggs retrieved greatly increases the chances of successful fertilization and embryo development. The stimulation phase usually lasts between 8 and 14 days and relies on close medical monitoring to ensure safety and effectiveness throughout the entire process. This monitoring ensures the patient responds optimally to the prescribed hormone regimen.
Pre-Stimulation Testing and Protocols
Before stimulation injections begin, a preparation phase ensures the ovaries are ready to respond predictably to the medications. This preparatory stage starts with a baseline evaluation around the beginning of the menstrual cycle, often Cycle Day 1 or 2. This evaluation involves a transvaginal ultrasound to check the ovaries and uterus. The baseline scan confirms the ovaries are in a “resting” state, meaning no large cysts or dominant follicles remain from a previous cycle that could interfere with the treatment.
Baseline blood work is performed simultaneously to measure hormone levels, most notably Estradiol (E2). A low Estradiol level, often under 60 pg/ml, is required to signal that the body’s natural hormones are suppressed and the patient is ready to start the stimulation drugs. Many protocols incorporate hormonal suppression, such as birth control pills or GnRH agonists, in the weeks leading up to the cycle. This suppression helps synchronize the growth of all the follicles, allowing the medical team to have better control over the timing and ovarian response. This synchronization is key to ensuring uniform follicle development once stimulation begins.
Determining the Specific Start Date
The precise day a patient starts the injectable stimulation medications is specific to the individual’s protocol and baseline testing results. For most standard protocols, the start date is scheduled for Cycle Day 2 or 3 (CD2 or CD3), immediately following a satisfactory baseline assessment. The confirmation of a thin uterine lining, low Estradiol levels, and the absence of problematic cysts are required to proceed. Starting on CD2 or CD3 is strategically timed to recruit the cohort of small follicles naturally available at the beginning of the menstrual cycle.
The type of protocol chosen, such as the Antagonist or Agonist protocols, influences the overall timeline, but the gonadotropin injections often begin around this CD2/CD3 window. For instance, in the Antagonist protocol, stimulation starts on CD2 or CD3, with a second drug added later to prevent premature ovulation. The goal is to start hormone delivery when the body is most receptive, maximizing the number of follicles that will grow simultaneously under the influence of the injected Follicle-Stimulating Hormone (FSH). The physician’s confirmation is necessary, as starting the medication prematurely or too late can negatively affect the cycle outcome and the quality of the eggs retrieved.
Daily Monitoring During the Stimulation Phase
Once stimulation injections begin, frequent monitoring visits are mandatory, usually lasting 8 to 13 days. This daily management is crucial for adjusting medication dosages, a process known as titration, to optimize egg growth and prevent complications like Ovarian Hyperstimulation Syndrome (OHSS). Monitoring involves a combination of transvaginal ultrasounds and blood tests, performed every one to three days.
The ultrasounds track the growth of the ovarian follicles, which are the fluid-filled sacs containing the eggs. Follicles are measured to ensure they are progressing appropriately, growing at an average rate of about 2 mm per day in the later stages. The goal is for a sufficient number of follicles to reach a mature size, generally between 17 mm and 22 mm, before the final step. Blood tests measure hormone levels, primarily Estradiol, which increases as the follicles grow and produce more estrogen. This hormonal evidence guides the doctor in determining if the medication dose needs to be raised, lowered, or maintained for the next 24 hours.
The Final Step: Administration of the Trigger Shot
The stimulation phase concludes when monitoring results indicate a sufficient number of follicles have reached the desired mature size. At this point, the final medication, known as the “trigger shot,” is administered to induce the eggs’ final maturation. This injection contains human chorionic gonadotropin (hCG) or a GnRH agonist, mimicking the body’s natural Luteinizing Hormone (LH) surge that precedes ovulation. The trigger shot ensures the eggs are fully ready for retrieval.
The timing of this final injection must be precisely followed, as it is directly tied to the scheduled egg retrieval. The trigger shot is administered exactly 34 to 36 hours before the retrieval procedure. This narrow window allows the eggs enough time to complete maturation without being released naturally from the ovary, which would make retrieval impossible.