Fertility treatments like in vitro fertilization (IVF) and intrauterine insemination (IUI) involve a “trigger shot.” This precisely timed injection prepares eggs for retrieval or natural ovulation. Its primary function is to signal the final stages of egg readiness.
Follicle Growth Before the Trigger
Ovarian follicles are small, fluid-filled sacs within the ovaries, each containing an immature egg. In a natural menstrual cycle, typically one dominant follicle matures and releases an egg. During fertility treatments, medications like follicle-stimulating hormone (FSH) are used to encourage multiple follicles to grow simultaneously. This process, known as ovarian stimulation, aims to produce several mature eggs.
Healthcare providers closely monitor follicle development using ultrasound and blood tests. This tracks follicle size and hormone levels, ensuring they reach an optimal size. Follicles are generally considered ready for the trigger shot when they reach a diameter of approximately 18-22 millimeters.
The Trigger Shot’s Role in Maturation
The trigger shot, commonly containing human chorionic gonadotropin (hCG), prepares the eggs. This hormone mimics the natural luteinizing hormone (LH) surge that typically occurs just before ovulation. This surge does not induce further follicle growth, but initiates the eggs’ final maturation.
Once the trigger shot is administered, the focus shifts from increasing follicle diameter to internal cellular changes. While some minimal growth might occur, follicles do not significantly increase in size after this injection. Instead, the signal from the trigger shot directs the eggs to undergo crucial developmental processes, making them viable for fertilization.
Post-Trigger Follicle Changes
After the trigger shot, biological changes begin within the follicles.
One significant event is the resumption of meiosis, a cell division process. During meiosis, the egg reduces its chromosome count from 46 to 23, preparing to combine with sperm’s genetic material. This reduction is essential for forming a healthy embryo with the correct number of chromosomes upon fertilization.
Simultaneously, the cumulus cells, which surround and support the egg within the follicle, undergo expansion. This expansion helps to detach the egg from the follicle wall, facilitating its eventual release or retrieval. These internal transformations are important for the egg’s fertilizability and developmental potential. The trigger shot ensures these changes occur, even if the follicle’s outer dimensions remain largely unchanged.
Crucial Timing for Retrieval or Insemination
Precise timing of the trigger shot is important for fertility treatment success. Egg retrieval for IVF, or intrauterine insemination (IUI), must be scheduled within a narrow window after the injection. This window is typically 34 to 36 hours post-administration, allowing eggs to reach optimal maturity without ovulating prematurely.
Mistiming the procedure can lead to suboptimal outcomes. If retrieval or insemination occurs too early, the eggs may be immature and unable to fertilize. Conversely, waiting too long can result in premature ovulation, where the eggs are released naturally from the ovaries before they can be collected for IVF.
Patients receive specific instructions for the trigger shot’s exact timing to ensure the best chance of success.