40w LaterGuide

During fertility treatment, you may hear about injections that help follicles grow and injections known as “trigger shots.” Although both may be used during the same treatment cycle, they have different purposes.

What do follicle-stimulating injections do?

Gonadotropins such as FSH stimulate follicles in the ovaries to grow and develop.

For people who do not ovulate regularly, gonadotropins may be used for ovulation induction, where the goal is usually to develop a mature follicle that can ovulate. In IVF, gonadotropins are used for ovarian stimulation, where several follicles are encouraged to develop for egg retrieval.

What does a trigger shot do?

Once follicles have developed appropriately, a trigger may be used to induce final oocyte maturation.

In ovulation induction or some IUI cycles, a trigger such as hCG can help induce final maturation followed by ovulation, allowing intercourse or IUI to be timed accordingly.

In IVF, the purpose is different. The trigger prepares the oocytes for egg retrieval by inducing final maturation. Egg retrieval is scheduled before spontaneous ovulation occurs.

Depending on the treatment protocol, hCG, a GnRH agonist or a combination may be used.

In simple terms

Follicle-stimulating injections → help follicles grow and develop

Trigger shot → induces final oocyte maturation and, in ovulation-induction treatment, helps initiate the process leading to ovulation

Does everyone need follicle-stimulating injections?

No. Treatment depends on the reason for infertility and whether ovulation occurs naturally. Some people may use oral ovulation-induction medications, while others may need gonadotropin injections.

In most conventional IVF stimulation cycles, gonadotropins are used to develop multiple follicles before egg retrieval.

Does everyone need a trigger shot?

Not necessarily. In naturally ovulating cycles, ovulation may be monitored without a trigger. In medicated cycles, a trigger may be used to coordinate final oocyte maturation and treatment timing.

In IVF egg-retrieval cycles, final oocyte maturation is required before retrieval, and the type of trigger is selected according to the treatment protocol and factors such as the risk of OHSS.

Can fertility injections increase the chance of twins?

In ovulation-induction and IUI cycles, developing multiple follicles can increase the risk of multiple pregnancy. Careful monitoring is therefore important, and treatment may be cancelled if too many follicles develop.

In IVF, multiple follicles are intentionally developed for egg retrieval. The risk of multiple pregnancy is more directly influenced by the number of embryos transferred, and single embryo transfer is an important strategy for reducing this risk.