Anomalies of the Placenta
November 11, 2010 · Leave a Comment
Anomalies of the Placenta
The placenta is a thick, disk-shaped organ. This organ approximately weighs 500 g and is 15 to 20 cm in diameter and about 1.5 to 3.0 cm thick. Normally, its weight is approximately one sixth of the fetus. Placenta is a very important structure for the fetus as it is involved in metabolic, circulatory, respiratory and endocrine functions.
It has two components, the maternal and fetal side. The maternal side is rough and it attaches to the uterine wall whilst the fetal portion is smooth with branching vessels covering the membrane-covered surface. This fetal structure is always examined for the presence of anomaly. Injury of placental portions can lead to serious fetal demise if left untreated.
Placenta succenturiata is a condition where one or more accessory lobes are connected to the main placenta by blood vessels. A succenturiate (accessory) lobe is either a second or third lobe that is quite smaller than the main lobe. This smaller succenturiate portion often has areas of disorder or atrophy. Such accessory lobes by themselves are of no major consequence to the fetus. However, they could produce problems on delivery.
Membranes in between the lobes of a succenturiate placenta can be torn during delivery resulting to massive blood loss. The small lobes can be retained in the uterus after delivery that could lead to severe maternal hemorrhage. This can be detected on inspection of the placenta at birth, where it appears torn at the edge. The remaining lobes must be removed from the uterus manually to prevent bleeding.
Normally, the chorionic membranes are not covering the fetal side of the placenta. With placenta circumvallata, the fetal side (smooth portion) is covered to some extent with chorion. The placenta has a central depression on its fetal surface to the edge where fetal membranes are attached. The umbilical cord enters the placenta at the normal site, however, the blood vessels end abruptly at the point where the chorion folds back to the surface. No fetal abnormalities are associated with this type of placenta but it is necessary to note its presence.
Naturally, the umbilical cord is inserted at the central portion of the placenta. Battledore placenta presents with a marginal cord insertion.
In this anomaly, the umbilical cord is inserted directly to the fetal membranes instead of inserting to the middle of the placenta. The cord then travels to the membranes of the placenta where the exposed vessels are not protected by Wharton’s jelly which poses a high risk of rupture. This condition may be associated with fetal anomalies.
If the umbilical vessels of a velamentous cord insertion cross the cervical os that causes it to be delivered first before the fetus is a condition called vasa previa. Cervical dilatation may tear the blood vessels that would result to fetal blood loss. If vasa previa is identified a cesarean section is done to deliver the fetus.
image from imaging.consult.com, library.med.utah.edu