Clinical Presentation

In general, not all placentas are sent for pathological examination. There is a variety of indications for placental examination including gross placental abnormalities, foetal death, foetal physical abnormalities, multiple births and maternal problems such as hypertension and diabetes.

Procedure and description for dealing with placentas

• the placenta is weighed and measured in three dimensions (cm).

• the umbilical cord is measured and its insertion into the chorionic plate described (central, eccentric, marginal or velamentous [membranous]).

• the cord is sectioned and the number of blood vessels noted. The normal umbilical cord contains two arteries and one vein. A segment of umbilical cord greater than 5 cm above the placental insertion should be examined as below this the arteries may fuse. Single umbilical cord arteries are associated with a number of fetal abnormalities.

- the presence of knots within the umbilical cord. If a true knot is present then differences in cord colour and diameter on either side of the knot are present.

- the state of the maternal surface of the placenta, i.e., whether it is complete or ragged.

- the state of the membranes, i.e., whether they are complete, ragged, translucent, opaque or dull (suggesting chorioamnionitis) or show meconium staining (this usually has a green colour). White or yellow nodules may indicate amnion nodosum.

• the placenta is carefully sectioned at 0.5-1 cm intervals and the presence of intervillous fibrin, infarcts (these appear as firm white or yellow areas), haematoma or any other focal lesion noted. The percentage of placenta involved by infarcts or haematoma is estimated.

• the presence of any other gross abnormality is described.

• in cases of suspected metabolic disease, the placenta may be sent to the laboratory unfixed and fresh tissue frozen.

Blocks for histology

• three representative sections of placental parenchyma.

• two cross sections of the umbilical cord.

• a membrane roll is prepared by cutting a long strip of membranes and leaving it attached to the placental disk. The membranes are then rolled around the disk and a cross-section is taken.

• any grossly abnormal area is sampled.

Histopathology report

• number of vessels within umbilical cord.

• cord insertion - central, eccentric, marginal, velamentous (membranous).

• maternal surface - complete, ragged.

• membranes - complete, ragged, translucent, opaque.

• infarcts - percentage of placenta area involved.

• intervillous fibrin - extent.

• maturity and outline of placental chorionic villi - consistent with gestation, accelerated or delayed, hydropic or molar changes.

• villous oedema - none, mild, moderate, severe.

• chorioamnionitis - absent, present, severity of. It implies ascending genitourinary infection.

• funisitis (inflammation of the umbilical cord) - absent, present, severity of.

• villitis - absent, present, severity of. It implies transplacental maternal infection.

• viral inclusions - absent or present. Immunohistochemistry may be required to confirm and characterise.

• foetal blood vessels - normal, abnormal.

• description of any other gross lesion.

Multiple gestation placentas

Multiple gestation placentas may be of four types.

1. Diamnionic, dichorionic separated twin placentas. These are separated twin placentas. The discs are completely separate. Each placenta is described separately.

2. Diamnionic, dichorionic fused twin placentas.

3. Diamnionic, monochorionic, fused twin placentas.

- In 2 and 3 there is a single placental disc with two umbilical cords. Common outer membranes are present.

4. Monoamniotic, monochorionic fused twin placentas.

- There are two umbilical cords but no dividing membrane.

Dividing membranes comprise two amnions and either one or two intervening chorions. Monochorionic membranes (monozygotic identical twins) divide easily whereas dichorionic (from either monozygotic or dizygotic [fraternal] twins) are more opaque and difficult to separate. Membrane distribution is studied histologically from both a non-separated area and the T zone point of attachment to the foetal surface (Figure 27.1). Vascular anastomoses between the two sides are also sought - these can lead to discrepancies in size and viability of the foetuses.

Non-separated membranes

Non-separated membranes

Twin Examination Medical
Figure 27.1. Examination of membrane distribution in twin pregnancy.

Placenta creta

This may be subdivided into placenta accreta, placenta increta and placenta percreta. In placenta accreta there is undue adhesion to the myometrial placental bed of the uterus with no intervening decidual layer. In placenta increta anchoring chorionic villi penetrate deeply into the myometrium. With placenta percreta chorionic villi infiltrate right through the wall of the uterus. With these conditions there is a risk of failure of normal postpartum placental separation. With placenta percreta, there is a risk of potentially fatal uterine perforation and haemoperitoneum. All these conditions may be diffuse or focal and the depth of penetration may vary in different areas of the placental bed. They are characterised by no intervening decidua between the uterine bed and the chorionic villi. Predisposing factors include placenta praevia, previous Caesarian section and previous placental retention requiring manual removal. Management of the complications of placenta creta may require hysterectomy.

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