The trigger shot is a precise injection of medication, most commonly human chorionic gonadotropin (hCG), used in fertility treatments like in vitro fertilization (IVF) and intrauterine insemination (IUI). This hormone mimics the body’s natural luteinizing hormone (LH) surge, which precedes ovulation. The shot’s purpose is to ensure the final, timely maturation and release of eggs, setting the stage for the next step of the fertility cycle. Confirming the shot’s success is important, as it represents the culmination of weeks of preparation and monitoring.
The Trigger Shot’s Immediate Action and Timing
The trigger shot is administered when ovarian follicles have reached an optimal size, typically confirmed through ultrasound monitoring. Once injected, the hCG hormone initiates the final maturation of the eggs within the follicles. This process prepares the eggs for fertilization.
The timing of the injection is highly regulated because it dictates the scheduling of subsequent procedures. Ovulation, the rupture of the follicles to release the eggs, is reliably expected approximately 36 to 40 hours after the shot. For IVF cycles, egg retrieval is scheduled at about 36 hours post-shot, just before the eggs would naturally ovulate. This narrow window ensures the retrieval of mature eggs.
Clinical Confirmation of Ovulation
The most objective way to determine if the trigger shot worked is through clinical monitoring performed by the fertility team. For IVF patients, the ultimate confirmation is the successful retrieval of mature eggs during the procedure. For both IVF and IUI cycles, doctors rely on two primary methods to confirm the physiological response.
The first method involves a transvaginal ultrasound, sometimes performed shortly after expected ovulation or before an IUI. The doctor looks for visual changes in the ovaries, specifically the disappearance of the large, fluid-filled follicles, indicating they have ruptured and released the egg. The presence of free fluid in the pelvis can also be an indirect sign of ovulation.
The second and most definitive clinical confirmation is a blood test to measure progesterone levels. The ruptured follicle transforms into a corpus luteum, which produces progesterone necessary to support a potential pregnancy. A progesterone level check is usually performed five to seven days after the trigger shot or IUI. It should show a significant rise, confirming the corpus luteum has formed and the shot successfully induced ovulation.
Navigating Home Pregnancy Tests and False Positives
A common source of confusion during the two-week wait is the use of home pregnancy tests (HPTs). Since the trigger shot is a dose of the hCG hormone, testing too soon will almost certainly result in a false positive reading. This occurs because the HPT detects residual hormone from the injection, not hCG produced by a new pregnancy.
The time it takes for the injected hCG to clear the body, known as the “washout period,” varies based on dosage and metabolism. Generally, it takes between 10 to 14 days for the hormone to exit the system completely. Testing before this timeframe provides an unreliable result.
Some patients choose to “test out the trigger” by taking daily HPTs to watch the positive line fade and disappear, confirming the injected hormone is gone. If a positive line reappears and darkens after the washout period, it suggests the presence of new, pregnancy-related hCG. The most reliable advice is to avoid home testing until the full waiting period has passed to prevent misinterpreting the results.
Final Confirmation of Cycle Success
The conclusive method for determining if the fertility cycle resulted in a pregnancy is the quantitative blood test, known as the Beta hCG test. This test is typically scheduled 10 to 14 days following the egg retrieval, IUI, or embryo transfer. Unlike a qualitative urine test, the Beta hCG test measures the exact concentration of the hormone in the bloodstream, expressed in milli-international units per milliliter (mIU/mL).
A positive result is generally considered an hCG level above 5 mIU/mL, though many clinics prefer a level above 25 mIU/mL for an initial positive. The initial number is important, but a single test cannot confirm viability. Viability is determined by a subsequent blood draw, usually performed 48 to 72 hours after the first. In a healthy pregnancy, the hCG levels should approximately double during this time, indicating successful implantation and growth.