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Trigger Shot Medically Reviewed

Last Updated: April 8, 2020

Definition - What does Trigger Shot mean?

A trigger shot is an injection of hormones that tells the ovaries to mature and release eggs. It works by kickstarting the process of egg maturation that is required for an egg to be capable of fertilization. Maturation involves a division (called meiosis) where an egg typically sheds 23 (or half) of its 46 chromosomes.

A trigger shot is used to time intrauterine insemination (IUI) or to prepare for an egg retrieval procedure as part of in vitro fertilization (IVF).

A trigger shot may also be called an hCG trigger shot or by the brand names Ovidrel, Pregnyl or Novarel.

FertilitySmarts explains Trigger Shot

In preparation for IUI or IVF, medication is taken to stimulate the production of multiple egg follicles. A trigger shot replaces the natural surge of luteinizing hormone signaling that causes eggs to undergo the final stage of maturation in preparation for egg retrieval or timed ovulation.

There are different medications that can act as a trigger shot.

Timing a Trigger Shot

Ultrasound monitoring and blood testing are done to determine when the follicles have reached the optimal number and size. Typically, having the majority of the follicles around 16mm to 22mm is considered ideal.

When a doctor determines that the appropriate time has arrived, a trigger shot is administered in the abdomen to start the process of final egg maturation, generally resulting in ovulation approximately 36 hours after the shot.

The timing of administering the medication is important because it controls the release of eggs. An egg retrieval procedure needs to happen prior to ovulation or with IUI, sperm should ideally be waiting for a mature egg.

hCG Trigger Shots and Pregnancy Tests

Home pregnancy tests measure natural levels of hCG in your urine, so when hCG is used as a medication it is advisable to wait at least 10 days after you receive the trigger shot to allow the synthetic hCG hormone to dissipate from your system.

FertilitySmarts uses high-quality sources to support the facts within our content including peer-reviewed studies, academic research institutions, medical organizations, and governmental organizations. Learn more about how we ensure content is accurate by reading our .
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