What is ovulation induction?

Ovulation induction (OI) refers to the stimulation of the ovaries, which should cause egg maturation and induce ovulation, in response to medications. OI is most commonly indicated for women with oligo-ovulation (abnormal ovulation) or anovulation (absent ovulation). 

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Women are born with all of the eggs that they will ever have. These eggs reside in follicles (sacs) inside the ovaries. When puberty begins, a female should undergo monthly menstrual cycles, during which one (sometimes two or more) egg matures and is ovulated (expelled from) the ovary. This egg then enters the Fallopian tube, where insemination and fertilization can occur. If this occurs, the fertilized egg (embryo) travels to the uterus and should implant into the uterine lining (endometrium). Therefore, irregular or absent ovulation can have a substantial impact on conception.

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Menstrual cycles are primarily controlled by the production and balance of reproductive hormones, and hormonal imbalances are the primary cause of ovulation disorders. Ovulation induction medications are administered to regulate the reproductive hormones and (hopefully) cause normal ovulation to occur. 

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If a woman’s body is responding properly to the medications, timed intercourse or an intrauterine insemination (IUI) can be performed during the menstrual cycle (shortly after ovulation occurs) in an attempt to achieve fertilization and a healthy pregnancy. Alternatively, ovulation induction can be performed prior to an IVF cycle to stimulate the growth of multiple follicles (in other words, the maturation of multiple eggs).

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Ovulation induction is a non-invasive, low-risk treatment option for certain cases of infertility, though it does carry the risks of multiple gestations (twins or more), ovarian hyperstimulation syndrome (OHSS), and injection site bruising, scarring, and inflammation.

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How do the Medications Work?

Common OI medications include:

1. Clomiphene Citrate (Clomid): this oral medication blocks estrogen from binding to its receptors in the brain (it tricks the brain into thinking that there is no estrogen in the body). As a result, the brain produces more of the hormones FSH and LH, which travel to the ovaries and cause:

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• Egg maturation
• Follicular growth (follicles grow in size as the eggs inside of them mature)
• Increased estrogen production as a result of the egg maturation and follicular growth

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Thus, this medication helps stimulate the maturation of one (or more) eggs, and it helps to maintain the body’s levels of FSH and LH.

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2. Aromatase inhibitors (Letrozole or Femara): this reversible enzyme inhibitor prevents the production of estrogen in the body. As with Clomid, this causes a rise in the production of FSH and LH from the brain, which travel to the ovaries and cause:

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• Egg maturation
• Follicular growth (follicles grow in size as the eggs inside of them mature)
• Increased estrogen production as a result of the egg maturation and follicular growth

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Aromatase inhibitors have gained popularity due to their reversible effects. Treatment with these medications also yields less multiple gestations and lower incidences of OHSS than Clomid. It is also a better option for women with PCOS.

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3. Gonadotropins (Follistim, Gonal-F, Menopur): these injectable medications consist of FSH and/or LH to increase the amount of these hormones in the body. Like the above medications, these hormones travel to the ovaries and cause: 

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• Egg maturation
• Follicular growth (follicles grow in size as the eggs inside of them mature)
• Increased estrogen production as a result of the egg maturation and follicular growth

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Because these medications often cause multiple eggs to mature, they are normally used for IVF rather than OI or IUI to prevent multiple gestations. These medications are also often administered with low-dose hCG, which mimics LH and aids in egg maturation.

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How do I know if my body is responding to the medications?

Throughout the ovulation induction process, you will be routinely monitored for the following:

• Ultrasound examinations of the ovaries will determine if follicles are growing in the ovaries and how large they are. It is assumed that eggs are inside of these follicles, though the eggs are too small to see.
• Blood tests to measure your hormone levels. These determine how your body is responding to the medications, how high your estrogen levels are (high amounts can lead to OHSS), and how close you are to ovulation. Alternatively, ovulation predictor kits or urine tests can also be used to track ovulation.

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What happens after ovulation occurs?

You will either engage in timed intercourse (sexual intercourse shortly after ovulation occurs, when women are “the most fertile”) or undergo an IUI procedure (a semen sample is injected into the uterus near the Fallopian tube).

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Roughly two weeks after timed intercourse or an IUI, a pregnancy test can be completed. You doctor will have more information about this process.

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Resources:

https://fertility.womenandinfants.org/treatment/ovulation-induction

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Ovulation Induction Techniques - StatPearls - NCBI Bookshelf (nih.gov)

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Ovulation Induction | Patient Education | UCSF Health

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