How Clomiphene Citrate & Letrozole Induce Ovulation
Plan your upcoming cycles and export calendar reminders (.ics) using our free ovulation tracker 6-cycle calendar.
In anovulatory cycles or unexplained subfertility, oral ovulation induction agents stimulate the central nervous system to boost follicular recruitment. Clomiphene citrate (Clomid) is a Selective Estrogen Receptor Modulator (SERM) that binds to estrogen receptors in the hypothalamus, deceiving the body into perceiving low estrogen levels. In response, the pituitary increases gonadotropin (FSH/LH) pulsatility to nurture follicular growth.
Conversely, Letrozole (Femara) is an aromatase inhibitor. It halts the peripheral conversion of androgens into estrogens, reducing circulating estradiol without depleting receptors in the cervix or uterus. Landmark randomized trials (Legro et al., NEJM) established Letrozole as the first-line medication for PCOS due to higher ovulation rates and significantly superior live birth outcomes.
For natural non-medicated months or post-treatment monitoring, you can forecast your natural baseline fertile window using our free online ovulation tracker.
Reproductive endocrinologists monitor follicular maturity via transvaginal sonography on CD10β12. An ideal follicle measures 18 to 22 mm in mean diameter with a trilaminar endometrial thickness of ≥7 mm prior to administering an hCG trigger.
Because sperm require 5 to 10 hours in the female reproductive tract to undergo capacitation, have intercourse the night of the trigger injection and again 36 hours later (the morning of anticipated ovulation) to ensure viable sperm are waiting in the fallopian tube.