PLACENTATION OF MULTIPLE PREGNANCIES

Blastocyst

• Embryonic stage of development that implants in uterus.
• Gives rise to all components of pregnancy including the placenta, chorionic membrane, amnion, fetus, yolk sac and stalk.
• The number of blastocysts implanting in the uterus determines the number of placentas that will develop
• The tissue from which embryonic placenta will develop precedes the formation of the amnion.
• If blastocyst implants far apart discrete placentas may be seen at birth however if they implant close to each other they may fuse and only a single mass will be seen at delivery.
• Placental Fusion in dichorionic pregnancy.
• Placental Fusion is common occurring in almost half dichorionic pregnancies. Close implantation sites and growth of the placental masses as the pregnancy progresses means in most dichorionic pregnancies means that in some patients the placentas will appear fused.

Monochorionic Diamnotic Twins · Thin intertwin membrane. · Single placenta situated posteriorly.
Dichorionic Diamniotic Twins · Thick intertwin membrane. · Placental fusion simulating a single placenta.
Dichorionic Placenta: - Anterior placenta twin A. - Posterior placenta twin B. - Separating membrane
Placental fusion indichorionic twin pregnancies