What key hormone is primarily responsible for regulating energy metabolism during pregnancy?

The hormone that plays a pivotal role in regulating energy metabolism during pregnancy is Human Chorionic Gonadotropin (hCG). This hormone is produced by the placenta shortly after implantation and is critical for maintaining the corpus luteum, which in turn sustains the production of progesterone during early pregnancy.

hCG contributes to maternal metabolic changes, ensuring that the developing fetus has a consistent supply of nutrients. Specifically, it influences how the body utilizes and stores energy, promoting a state that supports fetal growth and development. This regulation helps to safeguard against complications related to insufficient nutrient availability during pregnancy.

In contrast, while estrogen and progesterone are important for maintaining pregnancy and supporting the development of the fetus, they play different roles in the metabolic processes. Estrogen is involved in promoting uterine growth and regulating other reproductive functions, whereas progesterone primarily helps in maintaining the uterine lining. Oxytocin is primarily known for its role in childbirth and lactation, rather than energy metabolism during pregnancy.

Thus, hCG is the key hormone that directly influences energy metabolism, making it the correct answer.