The “trigger shot” is a final step in an In Vitro Fertilization (IVF) cycle. This injection induces the final maturation of eggs within the ovaries, preparing them for retrieval. It signals the culmination of the ovarian stimulation phase and directly precedes the egg retrieval procedure. The timing of this shot significantly impacts IVF success.
Ovarian Stimulation’s Role
The trigger shot is administered after a period of ovarian stimulation, a process where fertility medications are used to encourage the ovaries to produce multiple mature eggs, rather than the single egg typically released in a natural cycle. These medications, often containing follicle-stimulating hormone (FSH) and luteinizing hormone (LH), stimulate the growth of numerous fluid-filled sacs called follicles, each potentially containing an immature egg. The aim of this preparatory phase is to maximize the number of mature eggs available for retrieval, thereby increasing the chances of successful fertilization and embryo development in the laboratory.
Determining Optimal Trigger Timing
Determining the exact moment for the trigger shot relies on careful monitoring by fertility specialists. Ultrasound scans are regularly conducted to measure the size and number of developing follicles. Follicles are typically considered ready for triggering when they reach 17-20 millimeters in diameter. The goal is to have multiple follicles in this mature size range.
Alongside ultrasound monitoring, blood tests are performed to assess hormone levels, particularly estradiol and progesterone. Estradiol (a form of estrogen) levels naturally rise as follicles mature, indicating their readiness. While rising estradiol is a positive sign, progesterone levels are monitored to ensure they remain low before the trigger. A premature rise in progesterone can negatively affect the uterine lining’s receptivity for embryo implantation, potentially impacting pregnancy rates.
The timing of the trigger is individualized, tailored to each patient’s unique response to the stimulation medications. The aim is to trigger when most follicles are mature but before natural ovulation occurs.
Understanding Trigger Medications
The trigger shot is a hormonal injection designed to mimic the body’s natural luteinizing hormone (LH) surge, which prompts the final maturation and release of an egg. The most common medication used is human chorionic gonadotropin (hCG). hCG works by binding to LH receptors, initiating the final cellular division process (meiosis) in the eggs, preparing them for fertilization.
Another option is a Gonadotropin-Releasing Hormone (GnRH) agonist, such as Lupron. Lupron stimulates a natural surge of LH, leading to egg maturation. This type of trigger is often chosen for patients at higher risk of ovarian hyperstimulation syndrome (OHSS), as it can reduce this risk compared to hCG. These medications are typically administered as a subcutaneous injection, often self-administered at home.
From Trigger to Egg Retrieval
Following the trigger shot, a specific time window begins for the egg retrieval procedure. The trigger injection initiates the final maturation process, causing the eggs to detach from the follicle walls and become ready for collection. Egg retrieval is typically scheduled approximately 34-36 hours after the trigger shot is administered.
This precise timing allows the eggs to reach optimal maturity while ensuring they are retrieved before natural ovulation occurs. If the retrieval is performed too early, eggs may not be fully mature; if too late, the eggs might have already been released from the ovaries and become inaccessible.
The egg retrieval procedure is a minor surgical procedure, usually performed under sedation. A thin needle guided by ultrasound is used to aspirate the fluid and eggs from the ovarian follicles. Adhering strictly to the clinic’s scheduled time for the trigger shot and subsequent retrieval maximizes the chances of collecting viable, mature eggs.