International Board of Certified Lactation Consultant (IBCLC) Practice Exam

Which hormone is a known inhibitor of prolactin during pregnancy?

1. Oxytocin

2. Progesterone

3. Estrogen

4. Relaxin

The correct answer is: Progesterone

Progesterone plays a significant role during pregnancy, and one of its functions is to inhibit prolactin, a hormone crucial for milk production. Progesterone maintains the uterine lining and supports the pregnancy, but it also works in conjunction with estrogen to suppress prolactin secretion from the anterior pituitary gland during the course of the pregnancy. This inhibition is essential because prolactin levels need to be controlled to prevent lactation from interfering with the pregnancy itself. While oxytocin is involved in childbirth and milk ejection, it does not inhibit prolactin. Estrogen, though it has a stimulating effect on prolactin levels during the latter part of pregnancy, also participates in the overall hormonal regulation alongside progesterone. Relaxin primarily functions to facilitate childbirth by softening the cervix and relaxing the pelvic ligaments rather than influencing prolactin secretion directly.