Injectable contraceptives inhibit ovulation by–

RML PRE 2025

Pharmacology

Easy

Appeared in: RML PRE 2025

Explanation

The primary mechanism by which injectable contraceptives inhibit ovulation is through hormonal suppression of the hypothalamic-pituitary-ovarian (HPO) axis.
The steady dose of progestin provides negative feedback to the pituitary gland, reducing the frequency of Luteinizing Hormone (LH) pulses and suppressing the mid-cycle LH surge.
This prevention of the LH surge is the critical step that stops the ovarian follicle from rupturing, thus inhibiting the release of an egg (ovulation).
Follicle-Stimulating Hormone (FSH) is also lowered, which prevents the development of a dominant follicle.

Option B: This describes secondary mechanisms of action. While thickening cervical mucus and creating an atrophic endometrium are true effects of injectable contraceptives, they do not inhibit ovulation. They act as barriers to sperm and implantation, respectively.
Option C: This is another secondary mechanism. Hindering ovum transport affects the movement of the egg through the fallopian tube after ovulation might have occurred; it does not prevent the ovulation event itself.
Option D: This option is incorrect because, while all listed points are actions of injectable contraceptives, only one of them (preventing the LH surge) is the direct mechanism for inhibiting ovulation, which is what the question specifically asks.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Mechanism of action of injectable contraceptives as background academic context rather than a clinical decision trigger.
Understanding the primary mechanism is vital for patient education. A nurse can clearly explain that the injection's main job is to stop the ovaries from releasing an egg each month.
Knowledge of the secondary mechanisms (thickened mucus, endometrial changes) helps in counseling patients about common side effects like irregular bleeding or amenorrhea, which are due to the atrophic endometrium.
The prolonged suppression of the HPO axis explains why there can be a delayed return to fertility (6-9 months) after discontinuing the injections, a crucial point for family planning discussions.

How to Approach the Question

First, carefully read the question and identify the key concept being tested. The question specifically asks for the mechanism that 'inhibits ovulation'.
Analyze each option to determine if it directly relates to the process of ovulation.
Option A describes the hormonal cascade (FSH/LH suppression) that directly controls ovulation. This is a strong candidate.
Options B and C describe other contraceptive effects on the cervix, endometrium, and fallopian tubes. Recognize that these are secondary mechanisms that act at different points in the reproductive process, not on ovulation itself.
Evaluate Option D ('All of these'). Since options B and C do not inhibit ovulation, this option must be incorrect.
Conclude that the most precise and correct answer is the one that describes the direct hormonal prevention of the LH surge, which is Option A.

Concept Tested & Keywords

Q04Mgo8KC4DyXbpyjpifAg

E6 Pharmacology KD Tripathi Essentials 9e Part 1 p. 377-379

E6 Gynecology Williams p. 131-159

E6 Medicine Harrison 22e Part 2 p. 1057-1059