The question of how long a trigger shot stays in the body is really two separate questions: how long the medication is functionally active, and how long it remains detectable. A trigger shot is an injection, typically containing human chorionic gonadotropin (hCG), which is a hormone nearly identical in structure to the body’s natural luteinizing hormone (LH).
This medication serves a specific purpose in fertility treatments like In Vitro Fertilization (IVF) or Intrauterine Insemination (IUI). By administering a calculated dose, the injection creates a sudden surge that mimics the natural LH peak. This surge signals to the ovaries that the egg follicles are ready for the final stages of maturation and subsequent release. Brand names for these shots include Ovidrel, Novarel, or Pregnyl.
The Intended Timeline for Ovulation
The primary purpose of the trigger shot is to precisely control the timing of ovulation, which is necessary for coordinating fertility procedures. The injection is administered once monitoring confirms that the egg-containing follicles have reached an optimal size and maturity. This timing is meticulously planned, often down to the exact hour and minute, to ensure the best possible outcome for the cycle.
Following the injection, the medication initiates a cascade of events that culminates in the final preparation of the eggs. For an IUI cycle, the insemination procedure is typically scheduled to occur between 24 and 36 hours after the trigger shot is given. This window is timed to coincide with the predicted moment of ovulation, increasing the chances of the sperm meeting a newly released egg.
In an IVF cycle, the timing is even more precise to ensure the eggs are collected before they are released naturally. Egg retrieval is almost always scheduled for approximately 36 hours after the trigger shot. This narrow window allows the eggs to complete their final maturation process while still safely inside the follicles.
How the Medication Clears the Body
While the functional effect of the trigger shot is complete within 36 hours, the hormone itself remains in the bloodstream and urine for a much longer period. The duration the medication persists is described by its half-life, which is the time it takes for half of the drug to be eliminated from the body. The half-life of injected hCG is approximately 24 to 36 hours, meaning the concentration of the hormone reduces by half every one to one-and-a-half days.
The clearance rate depends on several factors, including the initial dosage administered and the individual’s metabolism and kidney function. If a high dose of hCG was used, it will take longer to fully clear compared to a lower dose. For example, a standard dose may take about 10 days to become undetectable, but a larger dose could take up to 14 days.
The liver metabolizes the hCG into its constituent parts, and both the intact hormone and its metabolites are primarily excreted through the urine. Because the process of elimination is gradual, the level of the hormone drops exponentially over time. A key distinction to understand is that the physical presence of the hormone in the body does not mean it is still actively causing ovulation. The initial surge completes its job quickly, but the residual hCG must be fully cleared before reliable testing can occur.
Interpreting Pregnancy Test Results
The lingering presence of the injected hCG creates a common complication for patients: the potential for a false positive on a home pregnancy test. Standard pregnancy tests work by detecting hCG in the urine, and they cannot distinguish between the hCG from a developing pregnancy and the residual hCG from the trigger shot. Testing too early will almost certainly result in a positive reading, even if conception has not occurred.
To avoid this misleading result, patients are typically advised to wait through a “test-out” or “wash-out” period before taking a home test. This wait time is usually 10 to 14 days post-injection, corresponding to the time required for the body to fully clear the hormone. Waiting for the hormone to exit the system ensures that any positive result seen is due to the rising hCG produced by an implanted embryo.
Some individuals choose to track the hormone’s clearance by testing daily, watching the line on a pregnancy test progressively fade to negative. If a negative test then becomes positive again, or if a very faint line starts to darken, it may suggest a true pregnancy. However, the most reliable confirmation of pregnancy always comes from a quantitative blood test (beta hCG) scheduled by the fertility clinic, which accurately measures the hormone’s level in the blood.