Circumvallate placenta - fetal membranes double back on the fetal side around the edge of the placenta. Occurs in about 1% of pregnancies.
Velamentous cord insertion - The umbilical cord inserts into the fetal membranes, then travels within the membranes to the placenta. Normally, the umbilical cord inserts into the middle of the placenta as it develops.
Marginal Insertion - occurs is about 7% of singleton pregnancies and 25% of twin pregnancies. The cord is located close to the edge of the placenta.
Bilobed placenta - A bilobed placenta is a placenta separated into two near equal lobes. Occurs in about 4% of pregnancies.