Letrozole is a medication used in fertility treatment to help stimulate ovulation and address fertility challenges. This article explores how letrozole works, the likelihood of conceiving twins, and general considerations for twin pregnancies.
How Letrozole Works
Letrozole functions as an aromatase inhibitor, blocking the aromatase enzyme. This enzyme converts androgens into estrogens. By inhibiting this conversion, letrozole lowers estrogen levels.
The temporary reduction in estrogen removes negative feedback on the hypothalamus and pituitary gland. This prompts the pituitary gland to increase its release of Follicle-Stimulating Hormone (FSH). Elevated FSH levels stimulate the ovaries to develop and mature follicles. While the goal is typically to encourage a single mature follicle, this increased stimulation can sometimes lead to the release of more than one egg.
The Likelihood of Twins with Letrozole
Letrozole slightly increases the chance of conceiving twins compared to natural conception. The general population’s twin rate is about 1%, while spontaneous twin pregnancies occur in 2-3% of cases. With letrozole, the chance of twins is typically below 5%, with some studies reporting rates around 3.4% or up to 10%.
Letrozole generally presents a lower risk of multiple pregnancies than another common fertility medication, clomiphene citrate (Clomid). While Clomid’s twin rate can be between 10% and 12%, letrozole’s rate is often considerably lower. When twins are conceived with letrozole, they are almost exclusively fraternal, or dizygotic, meaning they result from two separate eggs being fertilized by two separate sperm. This is a direct consequence of the medication potentially stimulating the release of more than one egg. Identical twins, conversely, arise from a single fertilized egg splitting and are not influenced by the use of letrozole.
What to Know About Twin Pregnancies
Twin pregnancies are associated with several increased considerations for both the birthing parent and the babies. For the parent, there is a higher likelihood of developing conditions such as preeclampsia, which involves high blood pressure, and gestational diabetes. Anemia is also more common, and there is an increased risk of preterm labor and birth, occurring before 37 weeks of gestation.
For the babies, prematurity is a significant concern, often leading to low birth weight and potential respiratory issues or other developmental considerations. Twin pregnancies also have a slightly higher risk of certain birth differences. In cases where identical twins share a placenta, there is a specific concern for Twin-to-Twin Transfusion Syndrome (TTTS), a condition where blood flow is unevenly distributed between the fetuses. Due to these increased considerations, twin pregnancies typically require more frequent and specialized monitoring, including regular ultrasound scans to assess growth, amniotic fluid levels, and placental function.