Amnion Chorion Placenta

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Figure 1.6. This view of the maternal surface in a term placenta shows the villous tissue to be complete, except for a small area of disruption at 5 o'clock. The placental cotyledons are vaguely outlined. A small amount of loose, soft, postpartum clot is present which should be removed prior to weighing and further examination. There are large and small yellow flecks of calcium.

point of rupture at the center of the roll, which is held in place with a pin and cut from the placenta. The weight of the still attached placenta facilitates this process. Rolls can also be made around a small piece of marginal placental tissue. The pin is unnecessary with hardening fixatives such as Bouin's. Rolls are difficult to make once the placenta has been fixed or if the membranes are severely disrupted or "slimy" from meconium (Figure 1.7, Figure 1.8).

7. The remaining membranes are trimmed away (with scissors or knife) and any loose soft clot is removed from the maternal surface. The placenta is now weighed, without cord or membranes, in a hanging pan or other balance. Measurements are taken of greatest diameters and thickness of the disk, and any extra lobes.

8. Transverse cuts are made through the maternal surface at 1-cm to 2-cm intervals. Lesions are measured and described. The degree of calcification and any unusual features such as villous color or texture are noted (Figure 1.9).

9. Representative pieces of the placenta are cut to include the margin, central villi from several cotyledons, and any significant gross lesions (Figure 1.10). Keeping the cord insertion area attached helps retain the amnion as the amnion is continuous with the surface of the cord. The samples are placed in formalin.

Fetal Membranes Amnion Chorion

Figure 1.7. The membranes of this normal, term placenta have been placed in their in situ uterine position. With a vaginal delivery, the minimal distance from the hole of rupture to the edge of the placental disk indicates the site of the placenta in the uterus. Shorter lengths indicate low-lying placentas. This shows a membrane roll being made from the rupture point to the margin of the placenta. It is then pinned, cut, and fixed. A larger length of membranes can be rolled and two sections cut from different areas.

Figure 1.7. The membranes of this normal, term placenta have been placed in their in situ uterine position. With a vaginal delivery, the minimal distance from the hole of rupture to the edge of the placental disk indicates the site of the placenta in the uterus. Shorter lengths indicate low-lying placentas. This shows a membrane roll being made from the rupture point to the margin of the placenta. It is then pinned, cut, and fixed. A larger length of membranes can be rolled and two sections cut from different areas.

Placenta Membrane Rolls
Figure 1.8. Histologic section of a cross section of a membrane roll shows the numerous layers visible by this technique. Amnion (A), chorion (C), and attached decidua (D) with small blood vessels are present.
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Figure 1.9. Mature placenta after transverse cuts (1.5 cm to 2 cm) have been made on the maternal surface in order to examine the villous tissue. The knife has a tendency to skip over firmer areas and simultaneous palpation of the villous tissue is necessary. The fetal surface is not usually cut and keeps the placenta somewhat intact.

Amnios Chorion

Figure 1.10. A transverse strip of placental tissue from the central region including the cord is routinely saved. This piece should be thin enough to adequate fix. Histologic blocks of villi including small surface vessels are taken from at least two separate areas in the placental midzone (boxes). These should not be from areas with thick subchorionic fibrin or hemorrhage as this masks inflammation. The placental margin has substantial artifact and is not ideal for assessing villous configuration. It may show more inflammation or decidual vascular change and can be submitted in addition. Placentas with significant pathologic processes require extra blocks to sample these.

Maternal surface-

Figure 1.10. A transverse strip of placental tissue from the central region including the cord is routinely saved. This piece should be thin enough to adequate fix. Histologic blocks of villi including small surface vessels are taken from at least two separate areas in the placental midzone (boxes). These should not be from areas with thick subchorionic fibrin or hemorrhage as this masks inflammation. The placental margin has substantial artifact and is not ideal for assessing villous configuration. It may show more inflammation or decidual vascular change and can be submitted in addition. Placentas with significant pathologic processes require extra blocks to sample these.

Placental Weight

Placental weight is not a precise measurement and will vary with the methodology of examination. It is affected by fixation, the presence of cord, membranes, and loose clot, the amount of blood retained, and the intactness of the maternal surface. Fresh refrigerated placentas lose a small amount of weight with storage, whereas formalin fixation leads to an increase, no more than 10% in either case. The value of placental weight is largely at the extremes, taking into account the gestational age and weight of the baby. A relatively heavy or light placenta often indicates an abnormal pregnancy. At term, the infant usually weighs about 7 to 8 times the placental weight. The ratio decreases earlier in gestation. Most term placentas weighing more than 750 grams or less than 350 grams will warrant histology. There are standard tables for placental weight by gestational age and by fetal weight as well as those with fetal-placental ratios by gestational age (Appendices B-1, B-2, and B-3).

Histologic Sectioning

Although it is possible to cut blocks from fresh placental tissue, this is far easier after some fixation has occurred. Sharp blades are important to keep the amnion on the placental surface intact. On most placentas cord (2 pieces from different sites), membrane roll, and two to three full thickness pieces of villous tissue including fetal and maternal surfaces are an adequate sample. The pieces of placental villous tissue should be from separate areas (different cotyledons), and not from the margin of the placenta, which frequently shows changes of diminished blood flow (Figure 1.10). The fetal surface of the section should include small blood vessels, and be free of substantial subchorionic clot or fibrin. Early changes of ascending infection are often masked in areas with thick sub-chorionic deposits. If the placental sections are too large to fit in the cassette, they will need to be divided. Additional representative sections of significant lesions or differences in villous character are also taken. En face blocks of the basal plate may be useful for evaluating maternal vas-culature. It is not necessary to section every infarct, hemorrhagic lesion, and so forth, as long as they are clearly identifiable grossly and adequately described. Blocking can be done by a trained technician. The specific type of fixation, processing, cutting, and staining may greatly alter the histology of the placental villous tissue. This is particularly important in the assessment of villous structure and maturation. Anyone looking at even a few placentas needs to become familiar with the appearance of villous tissue at different points in gestation as prepared in their histology lab.

Reports

For reports, the form on which the original gross information is recorded can often serve as the actual report or a master for rapid typing of reports. These forms can readily incorporate the microscopic exam and diagnoses. Some hospitals use placental check lists while in others reports are narrative. The special requirements of twin placentas should be either a separate form or incorporated into the singleton worksheet. (Appendix A1,2)

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Responses

  • gloria
    What is a dividing membrane?
    8 years ago
  • mirabella smallburrow
    Is the chorion the maternal surface of placenta?
    5 years ago
  • kirsty
    How to separate amnion and chorion for transplant?
    5 years ago
  • merimas
    How to get an amnion to separate from the chorion easier?
    3 years ago
  • Lara
    How to roll placental membranes?
    2 years ago
  • j
    How to separate amnion from chorion in a placenta?
    2 years ago
  • taija
    What happens if amnion os stripped on my placenta?
    5 months ago

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