Just like us human beings, the placental also has a lifespan. For human beings, it ranges from 60 to 100. For the placenta, it is 9 to 10 months (37 to 40+ weeks). With time and aging, the blood vessels thicken and calcium deposits in the lining, causing the vessels to be less elastic and less efficient in transporting oxygen. As a result, the baby can suffer diminished growth. It is important to monitor the baby closely during the 3rd trimester via a doppler.