Only when the site of detachment occurs on the side facing the cervical opening can the total amount of haemorrhaging be measured by vaginal bleeding. Using vaginal bleeding as a measurement of the severity of the placental abruption is therefore ineffective. The scale of haemorrhaging depends on the degree to which the placenta has separated from the uterine wall. In the case of partial placental separation, haemorrhaging can be minor. However, in the case of total placental separation haemorrhaging will be major and emergency delivery will typically be the course of action. Placental abruption causes blood loss from the mother and loss of oxygen and nutrients to the placenta occasionally leading to preterm labour. Other causes of placental abruption can be abdominal trauma or sudden decompression of amniotic fluid, however it is not uncommon for the cause of placental abruption to be unknown. Vasa praevia
Vasa praevia is the presence of unprotected foetal blood vessels running along the placenta and over the internal cervical opening. Vasa praevia is a very rare, presenting only 4:10,000 cases from the largest study of the condition. Risks of antepartum bleeding due to vasa praevia greatly increase during the third trimester of pregnancy during cervical dilation or placenta praevia. Vessel rupture is very likely in the event of a membranous rupture as foetal blood vessels arent protected by the umbilical cord of the placenta. In the event of foetal vessel rupture, antepartum haemorrhaging occurs however blood is lost from the foetal blood supply.
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.