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The fetal membranes are the four extraembryonic membranes, associated with the developing embryo, and fetus in humans and other mammals. They are the amnion , chorion , allantois , and yolk sac . [ 1 ]
The chorion and amnion membranes are labelled in this depiction of a growing fetus in the uterus. The amniotic sac consists of two parts: The outer membrane is the chorion. It is closest to the mother and physically supports the much thinner amnion. The chorion is the last and outermost of the membranes that make up the amniotic sac. [13]
Once the membranes are ruptured, bacteria may ascend and could lead to amnionitis and fetal infection. A premature rupture of membranes can have multiple effects on the fetus such as increasing their risk of prematurity and facing neonatal or perinatal complications. Rupture of membranes can affect ongoing labor management.
The inner of these membranes, the amnion, encloses the amniotic cavity, containing the amniotic fluid and the embryo. The outer membrane, the chorion, contains the amnion and is part of the placenta. On the outer side, the amniotic sac is connected to the yolk sac, the allantois, and via the umbilical cord, the placenta. [4]
A fetus surrounded by the amniotic sac which is enclosed by fetal membranes. In PROM, these membranes rupture before labor starts. The cause of PROM is not clearly understood, but the following are risk factors that increase the chance of it occurring. In many cases, however, no risk factor is identified. [10]
Circumvallate placenta is a rare condition affecting about 1-2% of pregnancies, in which the amnion and chorion fetal membranes essentially "double back" on the fetal side around the edges of the placenta. [1] After delivery, a circumvallate placenta has a thick ring of membranes on its fetal surface. [2]
The vessels are hence normally protected by Wharton's jelly, which prevents rupture during pregnancy and labor. [10] In velamentous cord insertion, the vessels of the umbilical cord are improperly inserted in the chorioamniotic membrane, and hence the vessels traverse between the amnion and the chorion towards the placenta.
Artificial rupture of membranes (AROM), also known as an amniotomy, is performed by a midwife or obstetrician and was once thought to be an effective means to induce or accelerate labor. The membranes can be ruptured using a specialized tool, such as an amnihook or amnicot, or they may be ruptured by the proceduralist's finger.