Velamentous insertion of umbilical cord is insertion of the cord away from the edge of the placenta. The vessels of the umbilical cord pass across the surface of the membranes between the membrane building the amniotic sac that surrounds and protects the embryo and the membrane that exists between the fetus and the mother and allows transfer of nutrients from the maternal blood to the fetal blood.
Velamentous insertion occurs in one percent of singleton preganancies and 15% in monochorionic twins and is common in triplets.
Velamentous insertion of the umbilical cord is caused by lateral growth of the placenta, which leaves the centrally located umbilical cord in an area that becomes atrophic, or when the cord implants in a place different than the one which will later develop as a placental mass.
Velamentous insertion of the umbilical cord can be diagnosed with ultrasound with sensitivity of 67% and specificity of 100% in the second trimester. In the first trimester diagnosis is possible through prenatal screening. It is associated with a lower maternal serum alpha-fetoprotein (AFP) and higher maternal serum human chorionic gonadotropin (hCG).
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elamentous insertion of the cord is associted with low birth weight, prematurity, abnormal fetal heart patterns in labor. Velamentous insertion can cause hemorrhage if the membranes are ruptured.
If the condition is detected, it is good to make all the necessary prenatal screening for other abnormalities, monitor the growth of the fetus with ultrasound in the third trimester, choose an elective cesarean to avoid vasa previa rupture or fetal distress if the velamentous insetion is in the lower segment.
Vasa previa is a very rare condition. It occurs in one out of 2000 or 3000 deliveries. It is associated with low-lying placenta, and multiple pregnancies.
Vasa previa is the positioning of the fetal vessels in the membrane in front of the presenting part of the fetus.