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The exact cause of placenta previa is unknown. It is hypothesized to be related to abnormal vascularisation of the endometrium caused by scarring or atrophy from previous trauma, surgery, or infection. These factors may reduce differential growth of lower segment, resulting in less upward shift in placental position as pregnancy advances. [11]
Vasa praevia is a very rare, presenting only 4:10,000 cases from the largest study of the condition. [16] Risks of antepartum bleeding due to vasa praevia greatly increase during the third trimester of pregnancy during cervical dilation or placenta praevia.
Besides placenta previa and placental abruption, uterine rupture can occur, which is a very serious condition leading to internal or external bleeding. Bleeding from the fetus is rare, but may occur with two conditions called vasa previa and velamentous umbilical cord insertion where the fetal blood vessels lie near the placental insertion site unprotected by Wharton's jelly of the cord. [11]
Placenta praevia or vasa praevia refers to the placenta or fetal blood vessels, respectively, covering or being located close to the opening of the uterus. More than half of women affected by placenta praevia (51.6)% have bleeding before delivery. [12] Vasa praevia occurs in about 0.6 per 1000 pregnancies. [13]
Velamentous Placenta: Normal umbilical cord insertion and velamentous umbilical cord insertion in pregnancy, with and without vasa previa. Specialty: Obstetrics Symptoms: Blood vessel compression, [1] [2] decrease in blood supply to the fetus, [2] [3] impaired growth and development of the fetus. [4] [5] Risk factors
It is thought that vasa previa arises from an early placenta previa. As the pregnancy progresses, the placenta tissue surrounding the vessels over the cervix undergoes atrophy, and the placenta grows preferentially toward the upper portion of the uterus. This leaves unprotected vessels running over the cervix and in the lower uterine segment.
Along with placenta previa and uterine rupture it is one of the most common causes of vaginal bleeding in the later part of pregnancy. [6] Placental abruption is the reason for about 15% of infant deaths around the time of birth. [2] The condition was described at least as early as 1664. [7]
Normally the maternal circulation and the fetal circulation are kept from direct contact with each other, with gas and nutrient exchange taking place across a membrane in the placenta made of two layers, the syncytiotrophoblast and the cytotrophoblast. Fetal-maternal haemorrhage occurs when this membrane ceases to function as a barrier and ...