Tuesday, September 18, 2018

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.

An annular (“girdle” or ring-shaped) is a  rare form of placenta which resembles a segment of a hollow cylinder. Sometimes a complex ring of placental tissue is seen. More commonly a portion of the ring undergoes atrophy resulting in a placenta which is approximately horseshoe-shaped. This type of placenta is probably a variant of placenta membranacea.
Its clinical significance is uncertain but it appears to be associated with a high incidence of both ante and postpartum bleeding. The fetus is often small for gestational age.

An example of abruptio placentae - premature separation of the placenta . A large abruptio placentae may result in poor growth of the infant and fetal blood loss.

Fetal surface of a placenta with a large chorangioma (hemangioma of the placenta). These infants may present with severe nonimmune hydrops fetalis. The majority of cases of hydrops fetalis are now
due to nonimmune causes.

A calcified, small placenta. This infant had severe intrauterine growth retardation at term as a result of poor fetal nutrition.

In velamentous insertion of the cord the umbilical vessels traverse the fetal membranes unsupported
by either the umbilical cord or by placental tissue. If tearing of these unsupported vessels occurs
before or during delivery, it can result in massive fetal blood loss.

Fetus born in a caul. Note that the membranes completely surround the fetus and that the umbilical cord (nuchal cord) encircles the neck twice. A cord around the neck once occurs in about 20%, and twice in about 2% of pregnancies. Whether the cord causes any problems depends on its tightness around the neck.

A hematoma of the umbilical cord (intrafunicular hemorrhage) resulted from a short umbilical cord.

A true knot in the umbilical cord of this fetus resulted in intrauterine death. The incidence of  true knots in the umbilical cord is 0.1 to 1%, and is strongly associated with long cords and other markers
of vigorous fetal activity. It is associated with about 10% of stillbirths. The knots must be very tight to obstruct blood flow. At the site of a long standing knot, such as in this fetus, there is a loss of Wharton’s jelly and a constriction of umbilical vessels. Wharton’s jelly probably prevents umbilical cord blood vessel compression by diffusing the pressure exerted by knots. The jelly is also slippery and this makes it difficult to maintain a knot.

The diagnosis of single umbilical artery is made by examining a section through the surface of the umbilical cord. This anomaly is present in 0.7 to 1.0% of single placentas and in 3 to 7.0% of multiple birth placentas. The incidence is low in black infants, but is increased in infants with associated congenital malformations. Further investigation is recommended if a single umbilical artery is associated with one other major anomaly.

This thin, narrow umbilical cord with total lack of Wharton’s jelly was present at birth in an infant with postmaturity and oligohydramnios. Cord compression is probably more frequent with a narrow cord, perhaps because the Wharton’s jelly does not “cushion” the cord.

This infant has a large cyst in the umbilical cord. The chemical composition of the fluid in this cyst was that of serum rather than urine. These cysts are thought to arise from the allantois.

No comments:

Post a Comment