What hormonal change triggers the onset of lactation?

• A. Increased oxytocin
• B. Increased prolactin after delivery
• C. Decreased estrogen levels
• D. Increase in progesterone levels

Answer: (B)

The hormonal change that triggers the onset of lactation is an increase in prolactin after delivery. Prolactin, a hormone produced by the anterior pituitary gland, plays a critical role in initiating and maintaining milk production in the breasts. During pregnancy, high levels of estrogen and progesterone typically inhibit milk production. After childbirth, the levels of these hormones decrease significantly, which allows prolactin to take effect, stimulating the mammary glands to produce milk for breastfeeding.

Although oxytocin is important for milk ejection, it does not directly trigger lactation. Instead, it facilitates the release of milk already produced in response to prolactin. Decreased estrogen levels occur post-delivery and contribute to the initiation of lactation, but it is the rise in prolactin that is the primary trigger. An increase in progesterone post-delivery is not associated with the onset of lactation, as progesterone levels actually drop significantly after the placenta is delivered, contributing to the conditions that allow prolactin to function effectively in milk production.