Which of the following hormones is NOT produced by the placenta during the first trimester?

The hormone that is not produced by the placenta during the first trimester is oxytocin. In the early stages of pregnancy, the primary hormones produced by the placenta include human chorionic gonadotropin (hCG), estrogen, and progesterone.

hCG is crucial for maintaining the corpus luteum and promoting the production of progesterone in the early weeks of pregnancy. Estrogen and progesterone are vital for maintaining pregnancy, supporting fetal development, and preparing the mother's body for childbirth and breastfeeding.

Oxytocin, on the other hand, is primarily produced by the posterior pituitary gland and plays a significant role during labor and postpartum, specifically in facilitating uterine contractions and milk ejection during breastfeeding. While oxytocin is important for managing labor and lactation, it is not a hormone synthesized by the placenta in the first trimester, which solidifies its status as the correct answer.