What effectively defines the ovarian hormone relaxin?

Relaxin is primarily known for its role in preparing the body for pregnancy. It is a hormone produced by the ovaries and the placenta, particularly during pregnancy, and it serves multiple important functions. One of the main actions of relaxin is to relax the ligaments and muscles of the pelvis, allowing the body to accommodate the growing fetus and facilitate childbirth. Additionally, relaxin helps to prepare the cervix for delivery by softening it.

While relaxin does play a role in various aspects of reproductive health, its most significant and notable function is its preparation of the body for pregnancy, making option A the most accurate choice. The other options focus on functions that are more directly related to the ovarian cycle, lactation, or the menstrual cycle, none of which capture the primary purpose of relaxin as effectively as the role it plays in preparing for pregnancy.