The Placenta, Its Membranes, and the Umbilical Cord

The human placenta is a highly sophisticated organ of interface between mother and fetus, often
referred to as the “gate-keeper to the fetus.” Careful examination of the placenta, its membranes,
and the umbilical cord can prove to be a valuable aid in the diagnosis and treatment of the
neonate. Gross examination of the placenta takes five minutes, and more sophisticated examination
should be considered when there is poor pregnancy outcome, recognizable malformations or
abnormalities, multiple gestation, extremes of amniotic fluid volume, severe intrauterine growth
retardation, short umbilical cord (< 32 cm), and profound acidemia.
The maternal surface of the placenta (decidual plate) is soft, spongy and dark red; and the fetal surface (chorionic plate) is shiny and steel blue to gray.
The placenta, membranes, and umbilical cord weigh approximately 400 to 600 g at birth.

Abnormalities in structure can result in an inefficient transport of oxygen and nutrients to the developing baby. Despite this importance, it is one of the least understood and investigated human organs.

A succenturiate (accessory) lobe is common and has no effect on the fetus. This occurs in about 3 to 5% of deliveries.  Its importance arises from the fact that it may be retained within the uterus and cause postpartum bleeding.

Fetal surface of a bipartite or bilobed placenta (placenta duplex). The two parts of the placenta
are of nearly equal size and this occurs in about 1% of deliveries. Note that the lobes are separated by membranes. The umbilical cord may insert into one or other lobe, or may insert between the two.

In a circumvallate (circummarginate) placenta the fetal surface may be reduced if decidual tissue has made its way between the amnion and chorion. This appears as a yellow, peripheral, hyalinized fold circumscribing the edge of the chorionic plate. This type of placenta has been reported to be a cause of antepartum bleeding and premature labor

This is an example of placenta membranacea (placenta diffusa). These placentas are rare. The ovum implants too deeply, the villae of the chorion fail to regress, and the placental tissue develops over the entire surface of the chorion. The placenta is very thin and is associated with poor fetal growth and antepartum hemorrhage. There may be previa type bleeding.