A 28-year-old woman who is exclusively breastfeeding her 4-month-old infant reports not having her menstrual period since delivery. Which hormone is primarily responsible for this physiological amenorrhea?

1. A

   Oxytocin

2. B

   Prolactin

3. C

   Estrogen

4. D

   Follicle-Stimulating Hormone (FSH)

Appeared in: HPSSC - 2015

Explanation

• Prolactin, secreted by the anterior pituitary gland, is the primary hormone responsible for milk production (lactogenesis).
• The physical stimulus of the infant suckling causes a surge in prolactin secretion, maintaining high levels in the mother's blood.
• Elevated prolactin directly inhibits the release of Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus.
• The suppression of GnRH leads to decreased secretion of Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) from the pituitary.
• Without adequate FSH and LH, the ovarian cycle is arrested; follicles do not mature, ovulation does not occur, and menstruation (amenorrhea) is the result.

Why Other Options Were Wrong

• Option A: Oxytocin is responsible for the milk ejection or 'let-down' reflex, which pushes milk out of the alveoli. It also causes uterine contractions but does not suppress the ovulatory cycle.
• Option C: Estrogen levels are actively suppressed during exclusive breastfeeding. High estrogen is required for the growth of the uterine lining and for triggering the LH surge for ovulation, both of which are inhibited in this state.
• Option D: Follicle-Stimulating Hormone (FSH) is necessary to stimulate the growth of ovarian follicles, but its secretion is inhibited by the high levels of prolactin. Therefore, its absence is a consequence of the process, not the primary cause.

Related Visual

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Hormonal regulation of lactation and its effect on the menstrual cycle (Lactational Amenorrhea) as background academic context rather than a clinical decision trigger.
• This physiological process is the scientific basis for the Lactational Amenorrhea Method (LAM), a natural form of family planning.
• For LAM to be over 98% effective as contraception, three specific criteria must be met: 1) the mother's menstrual periods have not returned; 2) she is exclusively or almost exclusively breastfeeding (day and night); and 3) her infant is less than six months old.
• Nurses play a crucial role in educating postpartum mothers that LAM is a temporary method and becomes unreliable once supplemental foods are introduced, menstrual bleeding resumes, or the infant reaches 6 months of age.

How to Approach the Question

• First, identify the key elements of the clinical scenario: a mother who is 'exclusively breastfeeding' and experiencing 'amenorrhea' (no period).
• The question asks for the hormone 'primarily responsible' for this condition.
• Recall the two main hormones involved in lactation: Prolactin and Oxytocin.
• Differentiate their primary roles. A helpful mnemonic is Prolactin is for milk Production, while Oxytocin is for milk Outflow (ejection).
• Consider the systemic effects of these hormones. The hormone responsible for continuous milk production (Prolactin) also has a central inhibitory effect on the reproductive axis.
• Evaluate each option: Prolactin's high levels suppress the entire ovulatory cascade. Oxytocin acts locally on the breast and uterus. Estrogen and FSH are the very hormones being suppressed by prolactin. Therefore, prolactin is the root cause.

Concept Tested & Keywords

• Concept Tested: Hormonal regulation of lactation and its effect on the menstrual cycle (Lactational Amenorrhea).
• Stem keywords: exclusively breastfeeding, 4-month-old infant, not having her menstrual period, physiological amenorrhea
• Lead-in keywords: Which hormone, primarily responsible
• Clinical cues: The term 'exclusively breastfeeding' is critical because the high frequency and intensity of suckling are necessary to maintain the elevated prolactin levels that suppress ovulation.
• Negative lead-in flag: false

Question ID

QCtl3sLstc4xgb1D9SunpA

Copy ID

Reference Book

E6 Physiology Guyton 4SAE Part 3 p. 69-71

E6 Obstetrics Williams pp. 48-68, 51-71