hCG Trigger Shots: How Do They Work?

If you’re trying to conceive with help from fertility treatments, your doctor may have spoken to you about administering hCG injections, also called “trigger shots”. This step is designed to get your body ready for ovulation right on schedule. Let’s go through the facts on hCG injections so you’ll know what’s coming, and how it can help you get pregnant.

hCG trigger shots: What’s in them, anyway?

First, let’s start with what’s in the trigger shots themselves. The hormone hCG (human chorionic gonadotropin) is the very same chemical released at the start of pregnancy by the cells that will eventually become part of the placenta.

In a natural conception, hCG tells the ovaries to continue pumping out progesterone, a hormone essential for maintaining the uterine lining. In this way, hCG is part of what triggers the complex physical changes of early pregnancy.

What are hCG trigger shots for?

egg cells
If you’re trying to conceive and undergo a course of ovarian stimulation, you will be given medicines such as clomiphene citrate (Clomid®) to help your ovaries develop and release mature egg cells.

A trigger shot of hCG can then be used to complete the process, and roughly 36 hours after an injection, your ovaries will be ready to ovulate. This process works because hCG is chemically similar to luteinizing hormone (LH), that triggers ovulation.

With an hCG trigger shot, you and your fertility care team can control as much as possible when your mature egg cell is released – meaning you will know the ideal timing for sexual intercourse, intrauterine insemination (IUI), or harvesting egg cells for use in IVF.

Can an hCG trigger shot fail?

An hCG trigger shot gets your body ready to ovulate, but in some cases, things might not go quite as planned. If your fertility troubles stem from a condition such as polycystic ovary syndrome (PCOS) or hyperprolactinemia, the follicles that contain egg cells may not rupture properly.

However, this doesn’t mean you won’t be able to release egg cells at all: your doctors may keep administering an hCG trigger shot until ovulation occurs while closely monitoring the follicle development.

Side effects of an hCG trigger shot

menstruation period stomachache abdominal pain
As hCG stimulates the development of ovarian follicles, the main side effect of hCG trigger shots as part of your fertility treatment is ovarian hyperstimulation syndrome (OHSS). This causes the ovaries to become swollen, and in severe cases may require treatment in hospital if fluid builds up in the chest and abdomen.

Some of the symptoms to watch out for include:

  • Nausea
  • Abdominal pain
  • Reduced urination
  • Extreme thirst

If you begin to show signs of OHSS, you need to stop the use of an hCG trigger shot and speak to your doctor.

hCG trigger shots and pregnancy tests

pregnancy test
The hCG in a trigger shot is the same hormone your body produces during pregnancy – which means there’s one problem to be aware of when you’re trying to conceive. Home pregnancy tests work by checking for the presence of hCG, and the hCG in a trigger stays in your system for some time.

If you take a pregnancy test during this time, a pregnancy test will read positive, whether or not an egg has actually implanted. To make sure you’re getting an accurate result of a pregnancy test, wait until 14 days after your hCG trigger shot.

Don’t let hCG trigger shots freak you out

infertility treatment doctor couple
The hCG trigger shot is an important part of trying to conceive through IUI, IVF and other fertility treatments. While your body produces this hormone naturally to support a pregnancy, when you take it as part of ovarian stimulation treatment, it has the effect of spurring ovulation.

Your fertility clinic will guide you through the process of using an hCG trigger shot, as well as the side effects to watch out for. If you’re nervous about using the trigger shot, think about asking your partner to help you out: you’re in this together, after all!