system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Twenty minutes after delivery of a newborn infant, a 22-year-old woman starts breastfeeding. Initially, the expressed milk is thick and yellowish. Three days later, the mother's breasts swell and the expressed milk becomes thinner and whiter. A decrease in maternal serum concentration of which of the following is most likely responsible for the observed changes in milk production?
assistant
Progesterone