Newer progestational contraceptives primarily act by :
**Core Concept**
The newer progestational contraceptives, such as depot medroxyprogesterone acetate (DMPA) and levonorgestrel-releasing intrauterine system (LNG-IUS), primarily act by inhibiting ovulation through a mechanism involving the hypothalamic-pituitary-gonadal axis.
**Why the Correct Answer is Right**
These contraceptives work by suppressing the secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus, which in turn reduces the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. This decrease in LH and FSH secretion leads to a reduction in ovarian follicular growth and ovulation. The LNG-IUS also has a local effect on the endometrium, causing atrophy and making it unsuitable for implantation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the primary mechanism of action of newer progestational contraceptives is not through direct inhibition of ovulation by the ovary. While some progestins may have a direct effect on the ovary, this is not the primary mechanism of action of the newer contraceptives.
**Option B:** This option is incorrect because the primary mechanism of action of newer progestational contraceptives is not through thickening of cervical mucus. While some progestins may have a local effect on the cervix, this is not the primary mechanism of action of the newer contraceptives.
**Option C:** This option is incorrect because the primary mechanism of action of newer progestational contraceptives is not through direct action on the endometrium. While some progestins may have a local effect on the endometrium, this is not the primary mechanism of action of the newer contraceptives.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the primary mechanism of action of newer progestational contraceptives is through inhibition of ovulation, which can be reversed when the contraceptive is discontinued. This is in contrast to older progestins, which may have a more direct effect on the ovary or endometrium.
**Correct Answer:** C. Inhibition of ovulation through suppression of GnRH secretion.