In Vitro Fertilization (IVF) is a fertility treatment that helps individuals and couples conceive by fertilizing an egg outside the body before implanting it into the uterus. The multi-step process includes ovarian stimulation, egg retrieval, fertilization, and embryo transfer. A key element in IVF is the “trigger shot,” a medication that prepares the body for egg retrieval. This injection ensures mature eggs are available at the appropriate time, aiming to improve successful fertilization.
Why the Trigger Shot is Essential in IVF
The trigger shot provides precise control over egg maturation and release in an IVF cycle. During ovarian stimulation, medications encourage the ovaries to produce multiple follicles. The trigger shot prevents premature ovulation, ensuring eggs are not released naturally before collection.
The controlled timing ensures eggs reach their final development stage and are ready for retrieval at an optimal moment. This synchronization maximizes viable eggs for fertilization. Without this injection, natural ovulation might occur unpredictably, reducing retrieval efficiency.
By initiating final maturation, the trigger shot allows fertility specialists to schedule egg retrieval with accuracy. This precise timing ensures collected eggs are mature and suitable for fertilization. This approach contributes to improving the chances of a successful pregnancy.
How the Trigger Shot Works in the Body
The trigger shot mimics the body’s natural luteinizing hormone (LH) surge, responsible for the final maturation and release of eggs from the follicles. This surge signals eggs to complete meiosis, reducing their chromosome number from 46 to 23. This prepares the egg to combine with sperm, forming a complete set of 46 chromosomes in the resulting embryo.
The most common medication for the trigger shot is human chorionic gonadotropin (hCG), similar to LH and binding to the same receptors. hCG promotes the final maturation of eggs and helps them detach from the follicle walls, moving into the follicular fluid. This detachment is important because during egg retrieval, a needle withdraws fluid from each follicle, which then contains the mature eggs.
Another type of trigger shot uses a Gonadotropin-Releasing Hormone (GnRH) agonist. This medication stimulates the pituitary gland to release a surge of both LH and FSH. This self-induced surge leads to final oocyte maturation and triggers ovulation, offering an alternative approach that can reduce the risk of ovarian hyperstimulation syndrome (OHSS), especially in patients with many follicles.
Taking the Trigger Shot and What Happens Next
The trigger shot is typically administered as an injection, often subcutaneously into the fatty tissue of the abdomen or thigh, though intramuscular injection into the buttocks is also possible. Most patients administer the shot themselves at home after receiving detailed instructions from their fertility clinic. Some medications, like hCG, may come as a powder that needs to be mixed with bacteriostatic water before injection, while others are ready to use.
The timing of the trigger shot is highly specific and is usually given approximately 34 to 36 hours before the scheduled egg retrieval. This precise window allows the eggs to undergo their final maturation without being released naturally from the ovaries. Missing the exact timing by a significant margin, such as 30 minutes or more, could compromise the retrieval and may require contacting the clinic immediately to adjust the retrieval schedule.
After receiving the trigger shot, some patients might experience mild side effects, including localized discomfort, redness, or itching at the injection site, usually resolving within a day. Other common sensations include mild abdominal discomfort, bloating, or pelvic pain, similar to ovulation symptoms. In some instances, a more significant complication called ovarian hyperstimulation syndrome (OHSS) can occur, where the ovaries become swollen and painful, potentially causing fluid buildup in the abdomen.
Fertility specialists choose between different types of trigger shots, primarily hCG or GnRH agonists, or sometimes a combination of both, based on the patient’s individual response to ovarian stimulation and their risk factors for OHSS. For example, a GnRH agonist might be preferred for patients at higher risk of OHSS due to its ability to minimize this complication. Following the trigger shot, the patient prepares for the egg retrieval procedure, which is performed under sedation to collect the mature eggs from the ovaries.