Medications to cause or enhance ovulation can be given orally or by injection. Clomiphene citrate and letrozole are the most commonly used oral medications, and are typically used for 5 days out of the cycle. They work indirectly by increasing the brain’s own hormones FSH and LH (gonadotropins) to stimulate the ovary to grow and release eggs. Side effects include menopausal type-symptoms and 8-10% chance of multiple pregnancy, but these risks appear to be lessened with letrozole. These medications are relatively inexpensive and do not require much in the way of ultrasound and blood monitoring.
Gonadotropins can also be given directly to the patient by injection. These injectable medications are associated with higher pregnancy rates than oral medications but also more risk of high order multiple pregnancy, ovarian hyperstimulation syndrome, and expense. Frequent ultrasounds and blood monitoring are needed for safety reasons. Sometimes letrozole is used in conjunction with gonadotropins for ovulation induction to decrease the cost and risk of hyperstimulation. Gonadotropins can be utilized for standard ovulation induction and for in-vitro fertilization (IVF), where the aim is to induce many eggs to grow. When given during an IVF cycle, gonadotropins are usually given in conjunction with other injectable medications called GnRH agonists or antagonists that prevent premature ovulation.
Patients respond differently to these stimulation methods, so medications may be adjusted to provide an optimal stimulation on an individual basis.
