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Can Femara cause twins?

Medically reviewed by Carmen Pope, BPharm. Last updated on June 29, 2023.

Official answer

  • Yes, taking Femara for fertility problems or PCOS does increase your risk of having twins.
  • The rate of twins with Femara treatment is around 3.4%.
  • The rate of twins in the general population is around 1%.

What is the risk of twins with Femara?

A 2014 study found that the rate of twins with Femara was 3.4% versus 7.4% for clomiphene, although this was not statistically significant. An analysis of multiple studies came to a similar conclusion. The twin rate in women not undergoing fertility treatment is around 1%.

What is Femara?

Femara (letrozole) is a prescription medication used for the treatment of breast cancer and it is also commonly used off-label to treat ovulation problems including polycystic ovary syndrome (PCOS) and unexplained infertility.

For fertility issues and PCOS, Femara is typically taken once a day for five days. It is usually started on day three or four of your monthly cycle (the first day of your monthly cycle is the first day of your period) and then you should ovulate about four to seven days after taking the last of the five pills. This means that If you started the pills on day three of your period then you should ovulate between days eleven to fourteen. Intercourse or intrauterine insemination is timed to coincide with ovulation.

How does Femara work for fertility problems?

When you take Femara, it blocks the action of the enzyme aromatase, which prevents the body from converting androgens into estrogens.

In women with fertility problems, blocking the action of aromatase and lowering levels of estrogen causes the body to increase the production of follicle-stimulating hormone (FSH), which stimulates the ovaries to produce eggs. Some women on Femara will release more than one egg because they produce more FSH while on Femara than a woman produces when ovulating naturally.

  • Femara (letrozole) Novartis Pharmaceuticals Corporation
  • Legro R, Brzyski R, Diamond M, et al. Letrozole versus Clomiphene for Infertility in the Polycystic Ovary Syndrome. N Engl J Med 2014; 371:119-129 DOI: 10.1056/NEJMoa1313517
  • Franik S, Eltrop SM, Kremer JA, Kiesel L, Farquhar C. Aromatase inhibitors (letrozole) for subfertile women with polycystic ovary syndrome. Cochrane Database Syst Rev. 2018;5(5): CD010287. Published 2018 May 24. DOI:10.1002/14651858.CD010287.pub3

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