Just What is Vasa Previa?
is a rare (1:3000), heartbreaking condition in which the fetal blood vessels, unsupported
by either the umbilical cord or placental tissue, traverse the fetal membranes (bag of
waters) across the lower segment of the uterus between the baby and the cervical opening.
The condition has a very high fetal mortality rate (50-100%) due to fetal exsanguination
resulting from fetal vessels tearing when the amniotic membranes rupture or because the
vessels become pinched off as they are compressed between the baby and the walls of the
Blood vessels feeding the baby normally travel from the placenta through the umbilical cord and into the baby's bellybutton. With velamentous insertion of the cord, or certain other placental abnormalities, parts of these blood vessels are unsupported instead of being imbedded in the placenta or umbilical cord. This in itself, is not necessarily life threatening or symptomatic. Babies with exposed vessels located between the baby and the cervical opening (vasa previa) are in serious trouble, however. Very often these exposed vessels tear or break, sometimes causing intermittent bleeding during pregnancy, other times causing a large bleed which compromises the baby immediately. Nathan lost more than half his blood supply in just a moment or two when my water broke. Since in vasa previa this very delicate vessel arrangement presents between the baby and the cervix, it is frequently the thinning and opening of the cervix and pressure from the baby on these vessels that brings about the child's demise. These vessels can also be pinched off by pressure from the baby and shut down the child's blood supply without necessarily causing any blood loss. Birth is disastrous for babies with vasa previa. These children share the womb with a time bomb that goes off at birth.
There are different types of vasa previa: multi-lobed placenta and velamentous insertion of the umbilical cord.
Velamentous Insertion of the umbilical cord - Normally, blood vessels run from the placenta via the umbilical cord to the baby. Velamentous insertion means that these veins travel across the amniotic membranes before they come together into the umbilical cord. Velamentous insertion happens in 1-2% of all pregnancies. The figures beneath show Velamentous insertion of Nathan's cord. Notice how the vessels run across the membranes. This is a delicate arrangement, but doesn't necessarily pose any threat (or symptoms, for that matter) during pregnancy.
Multi-lobed Placentas - The lobes of bilobed and trilobed placentas are separated by a membrane and are of equal or near equal size. There is no certain information on how multilobed placentas are formed. Because a bilobed placenta in one pregnancy is followed by greater chance of bilobed placenta in subsequent pregnancies, it is possible that some multilobed placentas are genetic in origin. The umbilical cord most often inserts into the membranes between the two lobes of bilobed placentas but in about one-third of cases it inserts into the larger of the two lobes.
A succenturiate (accessory) lobe is a second or third placental lobe that is much smaller than the largest lobe. Unlike bilobes, the smaller succenturiate lobe often has areas of disease or atrophy. The risk factors associated are advanced maternal age, primigravida, proteinuria in the first trimester of pregnancy, and major malformations in the fetus. The membranes between the lobes in such placentas can be torn during delivery, and the extra lobe can be retained after rest of the placenta has been delivered, with consequent postpartum bleeding.
Two consequences of multilobed placentas most often reported are bleeding in the first trimester of pregnancy, and a failure of one of the lobes to separate at delivery with consequent postpartum hemorrhage. There are also published reports that bilobed placentas increase in frequency with advanced maternal age and with a maternal history of infertility. Other risk factors include maternal cigarette smoking during pregnancy, the mother being over 34 years of age, excessive vomiting during the first trimester of pregnancy, diabetes, and one of the parents or a sibling having a chronic seizure disorder.
So What Can Be Done to SAVE Vasa Previa Babies?
When vasa previa is detected prior to labor, the baby has a much greater chance of surviving. Despite improvements in medical technology, vasa previa often remains unsuspected until fatal fetal vessel rupture occurs. When vasa previa is found, elective delivery by cesarean before labor begins can save the baby's life. Tests can be used to measure the maturity of the baby's lungs. With steroids the baby's lung maturity can be hurried along before the C-section. Investigation for the source of the blood is necessary when there has been hemorrhage before or during birth, especially when associated with fetal heart irregularities. Aggressive resuscitation of the neonate is necessary where fetal vessel rupture has occurred. Without these measures, the baby is almost sure to die.
Transvaginal ultrasound (an ultrasound view of the cervix) in combination with color Doppler (which can show blood flowing through veins) is the most effective tool in the diagnosis of vasa previa during pregnancy and should be utilized in patients at risk, specifically those with bilobed, succenturiate-lobed, and low-lying placentas, pregnancies resulting from in vitro fertilization, and multiple pregnancy. This color technique makes it possible to see whether the veins are imbedded the placenta or are crossing the cervical opening.
But what happens to the baby of an uneventful pregnancy with no risk factors or symptoms? Velamentous insertion - unlike other placental abnormalities, is not looked for and seldom found before delivery; but velamentous cord insertion is a definite risk factor for vasa previa. Velamentous insertion of the umbilical cord is said to have a 1:50-100 occurrence rate. Color Doppler ultrasounds should be done during all routine prenatal ultrasound exams to determine placental implantation of the cord and rule out velamentous insertion. This is not standard practice at this time. Transvaginal color Doppler ultrasounds should be done as a matter of course following the suspicion any implantation abnormalities. It only takes a moment to diagnose life...
For more information check out Nathan's vasa previa links page.
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