Oh, the endocrinology of pregnancy! It's basically a high-stakes hormonal relay race where the placenta eventually takes the baton from the ovaries to keep everything running smoothly.

Let's start with the "pregnancy announcer," hCG (human Chorionic Gonadotropin). It's produced by the syncytiotrophoblast as early as 8 days after fertilization. Its main job? Keeping the corpus luteum alive so it can keep pumping out progesterone until the placenta is ready to take over. I'll pull up a diagram showing how these hormone levels shift throughout the trimesters.