Progestin-only pills (minipills) primarily prevent pregnancy through which mechanism in compliant users with consistent timing?

• A Thickening of cervical mucus, impeding sperm penetration ✓
• B Suppression of ovulation in all cycles
• C Prevention of implantation by thinning the endometrium
• D Inhibition of acrosomal reaction of spermatozoa

Explanation

Traditional minipills (norethindrone 350 mcg) primarily work by thickening cervical mucus within 2–4 hours of ingestion, creating a barrier to sperm penetration—this is the predominant mechanism. Ovulation is suppressed in only 40–60% of cycles with traditional minipills, unlike combination OCP. The endometrial effect (impeding implantation) is secondary. The newer desogestrel-containing minipill (75 mcg desogestrel) suppresses ovulation in >97% of cycles and has a 12-hour missed-pill window compared to the 3-hour window for norethindrone minipills. The strict 3-hour dosing window for traditional minipills reflects the rapid decline of cervical mucus effect, making cervical mucus change the primary and critical mechanism.

Reference: Shaw's Textbook of Gynaecology, 17th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.