Fetal Surface

The fetal (chorionic or amnionic) surface, facing the amnionic cavity, has a glossy appearance because of the intact epithelial surface of the amnion. This membrane covers the chorionic plate, including the chorionic vessels.

The latter branch is a star-like pattern positioned centrifugally from the cord insertion over the fetal surface (Fig. 2.1, left). Where arteries and veins cross, the arterial branches are usually closer to the amnion; they cross the veins on their amnionic aspect. Wentworth (1965) reported that only about 3% show the opposite condition. According to Boyd and Hamilton (1970), the superficial position of one or few venous branches at points of arteriovenous crossing is not unusual.

In the vicinity of the larger chorionic vessels, the chorionic plate normally has an opaque appearance because an increased number of collagen fibers accompany the vessels. Those areas of the chorionic plate located between the chorionic vessels are mostly transparent and are dark lilac to black because maternal blood in the intervillous space shines through. Opaque spots (bosselations) or large opaque areas independent of chorionic vessels usually point to large subchorionic deposits of Langhans’ fibrinoid.

Near the placental margin, where the most peripheral branches of the chorionic vessels bend vertically toward the marginal villous trees, the transparency of the chorionic plate decreases, resulting in a largely incomplete, opaque subchorial closing ring that is a result of increased amounts of cytotrophoblast and collagen fibers (see Chapter 9). It connects the placenta with the membranes. In the case of a particularly broad and prominent subchorial closing ring, the specimen is called a placenta marginata. A placenta circumvallata is formed when the closing ring is peripherally undergrown by villous trees. In such cases, it does not represent the outermost margin of the placenta; rather, the membranes insert superficially from the fetal surface of the placenta.

Placental shape and cord insertion are sometimes regarded as structurally impressive but functionally unimportant parameters. Becker (1989) stressed that both are influenced by the intrauterine position of the placenta. According to Schultze (1887), the location of the cord insertion represents the epicenter of implantation. Eccentric or marginal cord insertion thus points to an eccentric implantation on the anterior or posterior uterine wall, which causes asymmetrical development of the organ for mechanical and nutritional reasons.

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