A 32-year-old man underwent conventional vasectomy 4 weeks ago. He reports he has been sexually active without any other contraception since the procedure and his wife has missed a period. What is the most likely explanation?
- A The vas deferens recanalised spontaneously, a complication seen in over 10 percent of cases
- B Vasectomy takes effect immediately and the pregnancy indicates surgical technical failure in almost all such cases
- C Sperm persisting distal to the ligated site can fertilise for up to about 12 weeks or 20 ejaculations after vasectomy ✓
- D His wife's missed period is due to the psychological stress of the procedure, not pregnancy
Correct answer: C. Sperm persisting distal to the ligated site can fertilise for up to about 12 weeks or 20 ejaculations after vasectomy
Explanation
Sterilisation by vasectomy is not immediately effective. Residual sperm remain in the reproductive tract distal to the site of ligation, and clearance takes roughly 12 weeks or about 20 ejaculations. Contraception must continue until semen analysis confirms azoospermia. Recanalisation occurs in well under 1 percent of cases, so option A overstates it greatly. Option B ignores this well-known window of residual fertility, which is the standard teaching point examined here.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.