The placenta is always examined after the birth of your baby. This is partially to make sure that the entire placenta was expelled after your gave birth, but it can also tell you a lot about your pregnancy, including things like your health and the gestational age of the pregnancy.
This photo is of the entire placenta including the amniotic sac. Notice that the amniotic sac is mostly still intact with the exception of the hole in which the baby was born through. You can see that there is not a lot of space to be had inside the amniotic sac. The baby who lived here weighed in at 8 pounds 9 ounces. Talk about a cramped space!
Photo © Robin Elise Weiss