Final answer:
Human placental lactogen primarily prepares the breasts for lactation by promoting mammary gland tissue growth and helps in regulating maternal glucose levels.
Step-by-step explanation:
The function of the hormone human placental lactogen (hPL) is multifaceted during pregnancy. One of its primary roles is to help prepare the breasts for lactation. It works towards this goal by stimulating maternal tissue growth, which leads to the enlargement of the uterus and the expansion and branching of mammary ducts. These changes help facilitate the eventual production and ejection of milk necessary for breastfeeding after birth. Additionally, hPL aids in regulating maternal glucose levels, ensuring an ample supply of glucose for the fetal development.