The “trigger shot” is a common step in fertility treatments, and understanding how long it remains in the body is a frequent concern for individuals undergoing these procedures. This injection contains human chorionic gonadotropin (hCG), a hormone also naturally produced during pregnancy. Because at-home pregnancy tests detect hCG, the presence of the trigger shot can lead to confusing results. This article explores the purpose of the trigger shot, how the body processes hCG, and the implications for timing a pregnancy test.
The Role of the Trigger Shot
The trigger shot is administered as part of various fertility treatments, such as in vitro fertilization (IVF) and intrauterine insemination (IUI). Its function is to mimic the natural luteinizing hormone (LH) surge, signaling the final maturation of eggs within the ovaries. This precise timing allows fertility specialists to schedule procedures like egg retrieval or IUI at the optimal moment for success.
The hCG in the trigger shot helps prepare the eggs for release and retrieval. For IVF, it facilitates meiosis, a cell division process that primes eggs for fertilization. In IUI cycles, the trigger shot helps pinpoint when ovulation is likely to occur, typically 24 to 36 hours after the injection, to maximize the chances of conception. The dosage of hCG can vary, with common units including 5,000, 6,500, or 10,000 IU, depending on the individual’s specific protocol and response.
How the Body Processes hCG
After administration, the body processes and eliminates the hCG from the trigger shot. The half-life of hCG ranges from 24 to 48 hours. This means that every one to two days, about half of the remaining hCG is cleared from the system. For example, if a 10,000 IU dose is given, roughly 5,000 IU would remain after one day, then 2,500 IU after two days, and so on.
The time it takes for hCG to be completely undetectable can vary among individuals, ranging from 10 to 14 days post-injection. Several factors influence this clearance rate, including the patient’s metabolism, the specific dosage of the trigger shot, and body mass index (BMI). Higher BMI, for instance, has been correlated with lower post-injection hCG serum concentrations, which might affect clearance times. While a significant portion of hCG is metabolized by the liver, approximately 20% is excreted through the urine.
Timing Your Pregnancy Test
Testing for pregnancy too soon after the trigger shot can lead to a false positive result. Home pregnancy tests detect hCG and cannot differentiate between hCG from a developing pregnancy and residual hCG from the trigger shot. This can create emotional distress and false hope.
To avoid false positives, wait at least 10 to 14 days after the trigger shot before taking an at-home pregnancy test. This waiting period allows sufficient time for the injected hCG to leave the system. While some tests claim early detection, the trigger shot can still interfere with accuracy. For the most reliable results, healthcare providers often schedule a blood test to measure hCG levels, which provides a more definitive answer.