A trigger shot, an injection of human chorionic gonadotropin (hCG), is a key component in fertility treatments like in vitro fertilization (IVF) or intrauterine insemination (IUI). This medication induces ovulation, the release of a mature egg from the ovary. Precise timing of this shot is important for maximizing success in assisted reproductive procedures.
The Typical Ovulation Window
Ovulation generally occurs about 36 hours after an hCG trigger shot, though the range can be 34 to 40 hours. This predictable timing allows fertility specialists to schedule procedures with optimal accuracy. For IVF egg retrieval, collection is typically scheduled around 36 hours post-injection, often before ovulation, to ensure eggs are gathered directly from follicles. For IUI, insemination is usually performed 24 to 36 hours after the shot to coincide with the anticipated release of the egg.
How the Trigger Shot Works
The trigger shot delivers human chorionic gonadotropin (hCG), a hormone resembling the body’s natural luteinizing hormone (LH). In a natural cycle, an LH surge triggers an egg’s final maturation and release. The hCG in the trigger shot mimics this natural LH surge, initiating egg development within stimulated follicles and prompting their release. This ensures eggs are mature for fertilization or retrieval.
Confirming Ovulation and Next Steps
Medical professionals use specific methods to confirm ovulation after a trigger shot. Ultrasound examinations can reveal signs like follicle rupture or fluid behind the uterus. Blood tests measuring progesterone levels also confirm ovulation, as progesterone naturally rises after an egg is released. For individuals undergoing IUI or timed intercourse, healthcare providers provide specific instructions for when to have the procedure or intercourse, typically within the 24 to 36-hour window following the shot. Following these instructions is important for optimizing conception chances.
Factors Influencing Ovulation Timing
While the 36-hour window is highly reliable, minor variations in ovulation timing after a trigger shot can occur. An individual’s physiological response to hCG, or the specific type and dosage of hCG used, might subtly influence timing. Fertility specialists carefully monitor follicle development through ultrasounds and hormone levels to determine the optimal moment for administering the trigger shot, typically when follicles reach 15 to 22 millimeters. This monitoring helps account for individual differences and ensures the shot is given at the most effective time.