If the foetus is developed enough caesarean sections are often recommended. Abnormal placental shape
Circumvallate placentaA circumvallate placenta refers to when the foetal membrane wraps twice around, over the foetal side around the edge of the placenta. This is to compensate for an undersized chorionic plate resulting in a decreased nutritional supply to the foetus. Thickening of the placental edge due to a circumvallate placenta can lead to placental abruption, causing antepartum haemorrhaging. Bilobed PlacentaA bilobed placenta has a cleavage in the middle dividing it into two lobes with membranous vessels branching in between. The exposed connecting membranous vessels present risk of rupturing due to limited protection from thrombosis and trauma. Bilobing of the placenta can be caused by placental implantation occurring over areas of uterine fibroid scarring, previous surgery, decreased blood supply or implantation occurring over the internal cervical orifice. Chances of vasa previa and placental abruption increase in the presence of a bilobed placenta due to decreased surface area for attachment to the uterine wall and the exposure of membranous vessels. Multilobed or Succenturiate PlacentaWhen a placenta has multiple lobes which are distal and not of equal size this is referred to as a succenturiate placenta. Distal lobes are connected by a placental artery and vein extending from the main placenta, which tends to be centrally located and is the largest in mass. At the time of contraction or delivery the connecting placental arteries and veins may rupture resulting in significant haemorrhaging.
To prevent further haemorrhaging patients with major placental praevia are recommended to have a caesarean delivery. Abnormal placentation
During pregnancy the layer of endometrium that attaches directly to developing blastocyst becomes the maternal portion of the placenta, also known as the decidua basalis. In the absence of a decidua basalis, trophoblast cells on the developing blastocyst form an abnormally deep attachment to the uterine wall, this is known as abnormal placentation. Abnormal placentation can categorised into 3 types, depending on the depth of infiltration of the chorionic villi into the uterine wall:
In placenta percreta, the chorionic villi have grow entirely through the myometrium and invade into the perimetrium. Placenta percreta results in the most intense haemorrhaging that can be expected caused by abnormal placentation. In the event of placental detachment from the uterine wall, the depth of chorionic villi attachment dictates the amount of haemorrhaging that can be expected. The chance of abnormal placentation increases in subsequent pregnancies, if there is scar tissue present from previous pregnancies. For example, previously undergoing a caesarean or placenta previa increases the likelihood of abnormal placentation, therefore increasing the chances of antepartum haemorrhaging. Placental abruption
Placental abruption occurs when the placenta detaches from the endometrium. Detachment causes antepartum haemorrhaging at the location of abruption. Depending on the site of detachment, haemorrhaging may or may not be apparent. If abruption occurs behind the placenta where blood cannot escape through the cervix, blood will pool and form a retroplacental clot.