Understanding how a posterior placenta works can help you feel more confident and prepared during your pregnancy. What is a Posterior Placenta ? The placenta is an organ that forms during pregnancy to provide oxygen and nutrients to the growing baby. It also removes waste products from the baby's blood. Wondering how the position of your placenta can affect your pregnancy, birth and baby? Here's everything you need to know about posterior placentas and what to do if you're told you have one. Learn what anterior and posterior placenta positions mean, how they affect kick counts, ultrasound, and delivery, plus when to call your provider.