40w LaterGuide

IVF often begins with ovarian stimulation, which uses medications to help multiple follicles develop before egg retrieval.

In a natural cycle, usually one follicle becomes dominant and releases an egg. During IVF, several follicles are encouraged to develop so that multiple eggs may be retrieved.

How is ovarian stimulation different from ovulation induction?

Ovulation induction is generally used to help people who do not ovulate regularly develop a follicle and ovulate. Ovarian stimulation for IVF aims to develop multiple follicles so that several eggs may be collected.

However, more follicles are not always better. An excessive ovarian response can increase the risk of ovarian hyperstimulation syndrome (OHSS), so treatment aims to balance an effective response with safety.

Why develop multiple follicles?

Not every developing follicle will produce a mature egg, not every retrieved egg will fertilize, and not every fertilized egg will develop into an embryo suitable for transfer or freezing.

Developing multiple follicles can therefore increase the chance of obtaining embryos for treatment. Additional suitable embryos may also be frozen for future frozen embryo transfer.

How does ovarian stimulation work?

Gonadotropins such as FSH are commonly used to stimulate the ovaries. During treatment, ultrasound is used to monitor the number and size of developing follicles, and blood tests may also be used when appropriate.

The medications, doses and duration of treatment are individualized according to factors such as ovarian reserve, age, previous response to stimulation and the response during the current cycle.

Preventing ovulation before egg retrieval

Medications are also used to prevent a premature LH surge and ovulation before the eggs can be retrieved. Common approaches include the GnRH antagonist protocol and the GnRH agonist long protocol.

GnRH antagonist protocols are widely used and are particularly recommended when a high ovarian response or increased risk of OHSS is expected. GnRH agonist long protocols are still used in selected situations.

There is no single protocol that is best for everyone.

Final oocyte maturation

When the follicles have developed appropriately, a trigger is given to induce final oocyte maturation before egg retrieval.

Depending on the treatment plan, an hCG trigger, a GnRH agonist trigger or a combination may be used. A GnRH agonist trigger can be particularly useful for reducing OHSS risk in appropriate GnRH antagonist cycles.

What happens after stimulation?

Egg retrieval is performed at a carefully scheduled time after the trigger. Retrieved eggs are fertilized with sperm and the resulting embryos are cultured.

Suitable embryos may be transferred during the same treatment cycle or frozen for a later frozen embryo transfer. If the ovarian response is very high and OHSS risk is increased, freezing all suitable embryos and transferring one later may be considered.

How is my stimulation protocol chosen?

Age, ovarian reserve markers such as AMH and antral follicle count, PCOS, previous responses to stimulation and the risk of OHSS can all influence the treatment plan.

The protocol or medication dose may even change between IVF cycles based on previous responses. Rather than comparing the number of injections or treatment duration with someone else’s, it is more useful to understand how your treatment is being adjusted to your own ovarian response.