If a singleton placenta, weigh and measure in three dimensions
(length, width, and depth). Measure the length and width of the
attached umbilical cord. Note the site of insertion (central,
eccentric, or velamentous-into the membranes). Make a fresh cut into
the cord and note the number of vessels (normal is three). Note the
presence of any true knots, false knots (convoluted fetal vessels),
areas of hemorrhage, and/or rupture sites. Follow the fetal vessels
along the placental surface (chorionic plate and confirm that they do
no extend beyond the placental edge into the membranes. Examine the
membranes for thickening, coloration (green pigment indicates
meconium), opaqueness. Examine the maternal surface to determine the
presence of all placental lobes (cotyledons). Look for areas of
infarcts (yellow plaques) or calcification. Breadloaf the placenta
substance and look for abnormal lesions. Submit one cross section of
the umbilical cord, one section of the placental parenchyma with fetal
surface (taken centrally) and a section of rolled fetal membranes. To
roll the membranes, remove a strip of membranes with a portion of
placental edge; roll the membranes towards the edge and pin the
membranes to the edge. Trim the membranes and placenta to fit the
cassette and either fix two or three hours
in Bouinís solution before placing into the cassette, or place the
tissue and pin into the cassette for fixation in formalin (tell the
Types of abnormal placentas:
with cord insertion at the placental edge.
Extrachorial placenta: Origin of the fetal
membranes inside the placental edge. Two types:
Circummarginate- membranes separate
directly off the fetal surface.
Circumvallate- membranes overlap
before separation, forming a thickened peripheral ring.
Succenturiate lobe-accessory placenta within
membranes connected to main lobe by bridging vessels. The presence of
fetal vessels within the membranes extending to a rupture site implies
a succenturiate lobe left inside the uterus.
Placentas of multiple gestations are best
described as a twin gestation with a fused single placenta. A placenta
with single membranes and two attached placentas represents a
monoamnionic monochorionic placenta (extremely rare), and can be
processed as a singleton placenta with an extra cord.
Twin placentas with a membranous septum represents
a diamnionic gestation. To determine whether the chorion is either
mono- or dichorionic, follow these principles
The septum in a dichorionic placenta is opaque and
thick. The septum in a monochorionic placenta is almost transparent.
Separating the components of the dichorionic septum
is difficult, and will demonstrate three layers. Separating the
components of a monochorionic septum is very easy, and demonstrates
Fetal vessels are often seen crossing from one
circulation to another in a monochorionic placenta. This can be best
demonstrated by injecting colored dye or milk into arteries and veins
from one cord, and determining whether the dye travels across the
septum to the other fetal vessels. Note any vein-vein, artery-artery,
or artery-vein anastomosis (arteries always run over veins).
Each side of the placenta with an umbilical cord
represents one gestation, and can be managed as a singleton placenta
described above. Sections should consist of umbilical cord, membrane
roll and placental section from each gestation,
and a membrane roll from the septum, processed as described above.