Controlled Ovarian Stimulation (COS)

COS uses injectable gonadotropins (FSH, LH or both) to override the body's natural single-follicle recruitment and develop multiple follicles at once. Monitoring via transvaginal ultrasound and estradiol blood tests guides daily dose adjustments over 8–14 days.

A GnRH agonist or antagonist is added to prevent premature ovulation. When lead follicles reach ~18–20 mm, a trigger shot (hCG or GnRH agonist) causes final egg maturation. Retrieval occurs 35–36 hours later. COS is the cornerstone of IVF and can also be used with IUI to increase the number of eggs available for fertilization.