Vasa praevia | |
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Other names | Vasa previa |
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Specialty | Obstetrics |
Vasa praevia is a condition in which fetal blood vessels cross or run near the internal opening of the uterus. These vessels are at risk of rupture when the supporting membranes rupture, as they are unsupported by the umbilical cord or placental tissue.
Risk factors include low-lying placenta, in vitro fertilization. [1]
Vasa praevia occurs in about 0.6 per 1,000 pregnancies. [1] The term "vasa previa" is derived from the Latin; "vasa" means vessels and "previa" comes from "pre" meaning "before" and "via" meaning "way". In other words, vessels lie before the fetus in the birth canal and in the way. [2]
Vasa previa is present when unprotected fetal vessels traverse the fetal membranes over the internal cervical os. These vessels may be from either a velamentous insertion of the umbilical cord or may be joining an accessory (succenturiate) placental lobe to the main disk of the placenta. If these fetal vessels rupture the bleeding is from the fetoplacental circulation, and fetal exsanguination will rapidly occur, leading to fetal death. 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. This has been demonstrated using serial ultrasound. Oyelese et al. found that 2/3 of patient with vasa previa at delivery had a low-lying placenta or placenta previa that resolved prior to the time of delivery. There are three types of vasa previa. Types 1 and 2 were described by Catanzarite et al. In Type 1, there is a velamentous insertion with vessels running over the cervix. In Type 2, unprotected vessels run between lobes of a bilobed or succenturiate lobed placenta. In Type 3, a portion of the placenta overlying the cervix undergoes atrophy. In this type, there is a normal placental cord insertion and the placenta has only one lobe. However, vessels at a margin of the placenta are exposed.
Vasa previa is seen more commonly with velamentous insertion of the umbilical cord, accessory placental lobes (succenturiate or bilobate placenta ), multiple gestation, and in vitro fertilisation pregnancy. In IVF pregnancies, incidence as high as one in 300 has been reported[ citation needed ]. The reasons for this association are not clear, but disturbed orientation of the blastocyst at implantation, vanishing embryos and the increased frequency of placental morphological variations in IVF pregnancies have all been postulated[ citation needed ].
It is recommended that women with vasa previa should deliver through elective cesarean prior to rupture of the membranes. Given the timing of membrane rupture is difficult to predict, elective cesarean delivery at 35–36 weeks is recommended. This gestational age gives a reasonable balance between the risk of death and that of prematurity. Several authorities have recommended hospital admission about 32 weeks. This is to give the patient proximity to the operating room for emergency delivery should the membranes rupture. Because these patients are at risk for preterm delivery, it is recommended that steroids should be given to promote fetal lung maturation. When bleeding occurs, the patient goes into labor, or if the membranes rupture, immediate treatment with an emergency caesarean delivery is usually indicated. [5] [6]
Placenta praevia is when the placenta attaches inside the uterus but in a position near or over the cervical opening. Symptoms include vaginal bleeding in the second half of pregnancy. The bleeding is bright red and tends not to be associated with pain. Complications may include placenta accreta, dangerously low blood pressure, or bleeding after delivery. Complications for the baby may include fetal growth restriction.
Oligohydramnios is a medical condition in pregnancy characterized by a deficiency of amniotic fluid, the fluid that surrounds the fetus in the abdomen, in the amniotic sac. It is typically diagnosed by ultrasound when the amniotic fluid index (AFI) measures less than 5 cm or when the single deepest pocket (SDP) of amniotic fluid measures less than 2 cm. Amniotic fluid is necessary to allow for normal fetal movement, lung development, and cushioning from uterine compression. Low amniotic fluid can be attributed to a maternal, fetal, placental or idiopathic cause and can result in poor fetal outcomes including death. The prognosis of the fetus is dependent on the etiology, gestational age at diagnosis, and the severity of the oligohydramnios.
Twin-to-twin transfusion syndrome (TTTS), also known as feto-fetal transfusion syndrome (FFTS), twin oligohydramnios-polyhydramnios sequence (TOPS) and stuck twin syndrome, is a complication of monochorionic multiple pregnancies in which there is disproportionate blood supply between the fetuses. This leads to unequal levels of amniotic fluid between each fetus and usually leads to death of the undersupplied twin and, without treatment, usually death or a range of birth defects or disabilities for a surviving twin, such as underdeveloped, damaged or missing limbs, digits or organs, especially cerebral palsy.
Placental abruption is when the placenta separates early from the uterus, in other words separates before childbirth. It occurs most commonly around 25 weeks of pregnancy. Symptoms may include vaginal bleeding, lower abdominal pain, and dangerously low blood pressure. Complications for the mother can include disseminated intravascular coagulopathy and kidney failure. Complications for the baby can include fetal distress, low birthweight, preterm delivery, and stillbirth.
Antepartum bleeding, also known as antepartum haemorrhage (APH) or prepartum hemorrhage, is genital bleeding during pregnancy after the 28th week of pregnancy up to delivery.
Bloody show or show is the passage of a small amount of blood or blood-tinged mucus through the vagina near the end of pregnancy. It is caused by thinning and dilation of the cervix, leading to detachment of the cervical mucus plug that seals the cervix during pregnancy and tearing of small cervical blood vessels, and is one of the signs that labor may be imminent. The bloody show may be expelled from the vagina in pieces or altogether and often appears as a jelly-like piece of mucus stained with blood. Although the bloody show may be alarming at first, it is not a concern of patient health after 37 weeks gestation.
Obstetrical bleeding is bleeding in pregnancy that occurs before, during, or after childbirth. Bleeding before childbirth is that which occurs after 24 weeks of pregnancy. Bleeding may be vaginal or less commonly into the abdominal cavity. Bleeding which occurs before 24 weeks is known as early pregnancy bleeding.
Prelabor rupture of membranes (PROM), previously known as premature rupture of membranes, is breakage of the amniotic sac before the onset of labor. Women usually experience a painless gush or a steady leakage of fluid from the vagina. Complications in the baby may include premature birth, cord compression, and infection. Complications in the mother may include placental abruption and postpartum endometritis.
Placenta accreta occurs when all or part of the placenta attaches abnormally to the myometrium. Three grades of abnormal placental attachment are defined according to the depth of attachment and invasion into the muscular layers of the uterus:
Postterm pregnancy is when a woman has not yet delivered her baby after 42 weeks of gestation, two weeks beyond the typical 40-week duration of pregnancy. Postmature births carry risks for both the mother and the baby, including fetal malnutrition, meconium aspiration syndrome, and stillbirths. After the 42nd week of gestation, the placenta, which supplies the baby with nutrients and oxygen from the mother, starts aging and will eventually fail. Postterm pregnancy is a reason to induce labor.
A vaginal delivery is the birth of offspring in mammals through the vagina. It is the most common method of childbirth worldwide. It is considered the preferred method of delivery, with lower morbidity and mortality than caesarean sections (C-sections).
Percutaneous umbilical cord blood sampling (PUBS), also called cordocentesis, fetal blood sampling, or umbilical vein sampling is a diagnostic genetic test that examines blood from the fetal umbilical cord to detect fetal abnormalities. Fetal and maternal blood supply are typically connected in utero with one vein and two arteries to the fetus. The umbilical vein is responsible for delivering oxygen rich blood to the fetus from the mother; the umbilical arteries are responsible for removing oxygen poor blood from the fetus. This allows for the fetus’ tissues to properly perfuse. PUBS provides a means of rapid chromosome analysis and is useful when information cannot be obtained through amniocentesis, chorionic villus sampling, or ultrasound ; this test carries a significant risk of complication and is typically reserved for pregnancies determined to be at high risk for genetic defect. It has been used with mothers with immune thrombocytopenic purpura.
Velamentous cord insertion is a complication of pregnancy where the umbilical cord is inserted in the fetal membranes. It is a major cause of antepartum hemorrhage that leads to loss of fetal blood and associated with high perinatal mortality. In normal pregnancies, the umbilical cord inserts into the middle of the placental mass and is completely encased by the amniotic sac. The vessels are hence normally protected by Wharton's jelly, which prevents rupture during pregnancy and labor. In velamentous cord insertion, the vessels of the umbilical cord are improperly inserted in the chorioamniotic membrane, and hence the vessels traverse between the amnion and the chorion towards the placenta. Without Wharton's jelly protecting the vessels, the exposed vessels are susceptible to compression and rupture.
Monoamniotic twins are identical or semi-identical twins that share the same amniotic sac within their mother's uterus. Monoamniotic twins are always monochorionic and are usually termed Monoamniotic-Monochorionic twins. They share the placenta, but have two separate umbilical cords. Monoamniotic twins develop when an embryo does not split until after formation of the amniotic sac, at about 9–13 days after fertilization. Monoamniotic triplets or other monoamniotic multiples are possible, but extremely rare. Other obscure possibilities include multiples sets where monoamniotic twins are part of a larger gestation such as triplets, quadruplets, or more.
Circumvallate placenta is a rare condition affecting about 1-2% of pregnancies, in which the amnion and chorion fetal membranes essentially "double back" on the fetal side around the edges of the placenta. After delivery, a circumvallate placenta has a thick ring of membranes on its fetal surface. Circumvallate placenta is a placental morphological abnormality associated with increased fetal morbidity and mortality due to the restricted availability of nutrients and oxygen to the developing fetus.
A cervical pregnancy is an ectopic pregnancy that has implanted in the uterine endocervix. Such a pregnancy typically aborts within the first trimester, however, if it is implanted closer to the uterine cavity – a so-called cervico-isthmic pregnancy – it may continue longer. Placental removal in a cervical pregnancy may result in major hemorrhage.
Placental expulsion occurs when the placenta comes out of the birth canal after childbirth. The period from just after the baby is expelled until just after the placenta is expelled is called the third stage of labor.
Early pregnancy bleeding refers to vaginal bleeding before 14 weeks of gestational age. If the bleeding is significant, hemorrhagic shock may occur. Concern for shock is increased in those who have loss of consciousness, chest pain, shortness of breath, or shoulder pain.
Emergency childbirth is the precipitous birth of an infant in an unexpected setting. In planned childbirth, mothers choose the location and obstetric team ahead of time. Options range from delivering at home, at a hospital, a medical facility or a birthing center. Sometimes, birth can occur on the way to these facilities, without a healthcare team. The rates of unplanned childbirth are low. If the birth is imminent, emergency measures may be needed. Emergency services can be contacted for help in some countries.
The anomaly scan, also sometimes called the anatomy scan, 20-week ultrasound, or level 2 ultrasound, evaluates anatomic structures of the fetus, placenta, and maternal pelvic organs. This scan is an important and common component of routine prenatal care. The function of the ultrasound is to measure the fetus so that growth abnormalities can be recognized quickly later in pregnancy, to assess for congenital malformations and multiple pregnancies, and to plan method of delivery.