A breastfeeding mother remains amenorrhoeic six months postpartum despite not using contraception. The mechanism of lactational amenorrhoea is:

• A Suckling-induced prolactin suppresses hypothalamic GnRH pulsatility, blocking LH and FSH release ✓
• B Oxytocin released during feeding directly suppresses pituitary gonadotrophs
• C Milk production consumes all circulating cholesterol, preventing ovarian steroidogenesis
• D Prolactin downregulates endometrial progesterone receptors, preventing implantation

Explanation

Frequent suckling raises prolactin, and elevated prolactin inhibits kisspeptin/GnRH pulsatile secretion, suppressing LH pulses needed for follicular development and ovulation. This hypothalamic suppression, not any direct pituitary or uterine action, accounts for lactational amenorrhoea and its contraceptive reliability when feeds are frequent and exclusive. Oxytocin mediates milk ejection and uterine contraction but has no direct antigonadotrophic effect, ruling out B. Options C and D describe mechanisms that do not exist physiologically.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.