Which organ serves as the primary site for fetal development?

The uterus serves as the primary site for fetal development due to its unique structure and functions. It is a muscular organ that can expand and contract, providing a suitable environment for a developing fetus. The inner lining of the uterus, called the endometrium, thickens in preparation for implantation and nourishment of an embryo. This organ is specifically designed to support pregnancy by providing the necessary blood supply, nutrients, and space for the growing fetus, allowing it to develop over the course of nine months. In contrast, the ovary is responsible for the production of eggs and hormones, the vagina serves as the birth canal and reproductive tract, and the fallopian tubes are the pathways through which eggs travel to the uterus and where fertilization occurs, but none of these structures support fetal development like the uterus does.