Understanding:
We need to identify the contraceptive method that works by preventing ovulation through suppression of the hypothalamo-pituitary axis.
Step 1: Mechanism of combined oral contraceptive pills
Combined oral contraceptive pills contain synthetic oestrogen and progesterone (or progesterone alone in mini-pills). When taken regularly, these hormones exert negative feedback on the hypothalamus and anterior pituitary gland. This suppresses the secretion of GnRH from the hypothalamus and subsequently reduces the secretion of FSH and LH from the anterior pituitary. Without the LH surge, ovulation does not occur. This is the primary mechanism of action.
Step 2: Mechanism of Copper-T
Copper-T is an intrauterine device (IUD) that works primarily by creating a hostile environment in the uterus (copper ions are spermicidal and affect sperm motility and viability) and by preventing implantation. It does NOT prevent ovulation.
Step 3: Mechanism of condom
Condoms act as physical barriers, preventing sperms from reaching the ovum. They have no effect on the hormonal axis and do not prevent ovulation.
Step 4: Mechanism of tubectomy
Tubectomy is a surgical procedure in which the fallopian tubes are cut and ligated (tied). This prevents the ovum from reaching the uterus and prevents fertilisation. It does not affect the hormonal axis or ovulation.
Answer:
Combined oral contraceptive pills prevent ovulation by suppressing the hypothalamo-pituitary axis through negative feedback of synthetic oestrogen and progesterone.
Combined oral contraceptive pills
Quick Tip:
A useful classification: barrier methods (condom, diaphragm) → prevent sperm-egg meeting; hormonal methods (pills) → prevent ovulation; IUDs (Copper-T) → prevent fertilisation/implantation; surgical methods (vasectomy/tubectomy) → permanent blockage.
