At what stage does the umbilical cord and placenta develop?

The umbilical cord and placenta develop during the embryonic stage of prenatal development. This stage occurs from approximately the second to the eighth week after conception. During this time, the fertilized egg, now called a zygote, implants into the uterine wall and undergoes rapid cell division and differentiation. Tissues begin to form, including those that will develop into the placenta and umbilical cord, which serve crucial roles in nourishing the embryo and facilitating the exchange of waste and gases between the mother and the developing fetus.

As the embryo grows, the placenta forms to connect to the developing baby's circulatory system through the umbilical cord, making it vital for the embryo's survival and development. Other stages, such as the germinal stage (which focuses on the initial cell division and implantation) and the fetal stage (where major organ systems continue to develop and mature), do not involve the formation of these structures. The postnatal stage pertains to development after birth and thus is not relevant to the development of the umbilical cord and placenta.