The placenta begins to form shortly after the fertilized egg implants in the uterine wall, which typically occurs around 7 to 10 days after conception. At this early stage, the outer cells of the blastocyst start developing into the placenta, while the inner cells become the embryo. The placenta continues to grow and develops into a functioning organ by about week 12 of pregnancy, at which point it takes over the nourishment and hormone production necessary for the developing baby. The placenta continues to mature and increase in size throughout the pregnancy, considered fully mature by around 34 weeks.
In summary:
- Placental development starts immediately after implantation (~7 to 10 days post-conception).
- By around week 12, the placenta is formed and functioning.
- It grows and matures throughout the pregnancy until about week 34.
This timeline ensures the placenta supports fetal growth from very early in pregnancy onward.
