Placental Anatomy & abnormalities:A detailed review Normal Placenta The usual term placenta is about 22 cm in diameter and 2.0 to 2.5 cm thick. It generally weighs approximately 470 g (about 1 lb). However, the measurements can vary considerably, and placentas generally are not weighed in the delivery room. The maternal surface of the placenta should be dark maroon in color and should be divided into lobules or cotyledons. The structure should appear complete, with no missing cotyledons. The fetal surface of the placenta should be shiny, gray and translucent enough that the color of the underlying maroon villous tissue may be seen. At term, the typical umbilical cord is 55 to 60 cm in length,3 with a diameter of 2.0 to 2.5 cm. The structure should have abundant Whartons jelly, and no true knots or thromboses should be present. The total cord length should be estimated in the delivery room, since the delivering physician has access to both the placental and fetal ends. The normal cord contains two arteries and one vein. During the placental examination, the delivering physician should count the vessels in either the middle third of the cord or the fetal third of the cord, because the arteries are sometimes fused near the placenta and are therefore difficult to differentiate. Fetal membranes are usually gray, wrinkled, shiny and translucent. The membranes and the placenta have a distinctive metallic odor that is difficult to describe but is easily recognized with experience. Normally, the placenta and the fetal membranes are not malodorous. Abnormalities of the Placenta Succenturiate lobe.(fig.a) Bilobed placenta.(fig.b) Evaluating placental completeness is of critical, immediate importance in the delivery room. Retained placental tissue is associated with postpartum hemorrhage and infection. The maternal surface of the placenta should be inspected to be certain that all cotyledons are present. Then the fetal membranes should be inspected past the edges of the placenta. Large vessels beyond these edges indicate the possibility that an entire placental lobe (e.g., succenturiate or accessory lobe) may have been retained. All or part of the placenta is retained in placenta accreta, placenta increta and placenta percreta. In these conditions, the placental tissues grow into the myometrium to lesser or greater depths. Manual exploration and the removal of retained placental tissue are necessary in these cases. PLACENTAL SIZE Placentas less than 2.5 cm thick are associated with intrauterine growth retardation of the fetus.4 Placentas more than 4 cm thick have an association with maternal diabetes mellitus, fetal hydrops (of both immune and nonimmune etiology) and intrauterine fetal infections.5(pp423–36,476,542–613) An extremely thin placenta may represent placenta membranacea. In this condition, the entire uterine cavity is lined with thin placenta. Placenta membranacea is associated with a very poor fetal outcome. PLACENTAL SHAPE Extra placental lobes are important, primarily because they may lead to retained placental tissue. Blood may be adherent to the maternal surface of the placenta, particularly at or near the margin. If the blood is rather firmly attached, and especially if it distorts the placenta, it may represent an abruption. The dimensions and volume of the placenta should be estimated.
Posted on: Sun, 28 Dec 2014 17:55:26 +0000
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