Placenta previa is a pregnancy complication where the placenta, an organ providing oxygen and nutrients to the fetus, implants in the lower part of the uterus. This positioning results in the placenta partially or completely covering the cervix, which is the opening to the birth canal. This condition can lead to complications during pregnancy and childbirth, often requiring careful medical management.
What is Placenta Previa
The placenta is a temporary organ that develops in the uterus during pregnancy, forming a connection between the mother and the developing baby. Normally, it attaches to the upper part of the uterus, away from the cervix, allowing a clear path for delivery.
Placenta previa is categorized into different types based on its position relative to the cervix. In complete placenta previa, the placenta entirely covers the cervix, blocking the baby’s exit. Partial placenta previa involves the placenta covering only a portion of the cervix. Marginal placenta previa occurs when the placenta’s edge is at the edge of the cervix or within 2 centimeters of the internal cervical opening, but does not cover it. A low-lying placenta is positioned in the lower uterine segment but not directly over the cervix.
How Placenta Previa is Identified
The most common symptom of placenta previa is painless vaginal bleeding, typically presenting as bright red blood. This bleeding often occurs in the second or third trimester, usually after 20 weeks of gestation, and can range from light spotting to heavy flow. The bleeding may stop and return later, sometimes becoming heavier as the pregnancy progresses.
Placenta previa is primarily diagnosed through ultrasound examinations, often during a routine prenatal anatomy scan around 20 weeks of pregnancy. An initial diagnosis may be made with an abdominal ultrasound, and a transvaginal ultrasound may be used for more precise imaging of the placenta’s location relative to the cervix.
Early diagnoses, particularly of a low-lying placenta, often resolve on their own as the uterus grows and stretches, causing the placenta to move upwards and away from the cervix. If the placenta moves sufficiently, a vaginal delivery may become possible. However, if the placenta remains close to or covering the cervix in later stages of pregnancy, the diagnosis of placenta previa persists.
Managing Placenta Previa During Pregnancy
Management of placenta previa aims to extend the pregnancy as long as safely possible to allow for fetal development, while minimizing complication risks. If no bleeding is present, healthcare providers recommend avoiding activities that could trigger bleeding or contractions. This includes refraining from sexual intercourse, douching, or using tampons, as well as limiting strenuous exercise, heavy lifting, or prolonged standing.
Close monitoring through regular ultrasound examinations is standard to track any changes in the placenta’s position. If bleeding occurs, hospitalization may be necessary for continuous monitoring of both the mother and the baby. During hospitalization, intravenous fluids and blood transfusions may be administered for significant blood loss.
Corticosteroids, such as betamethasone or dexamethasone, are often administered if preterm delivery is anticipated, especially before 37 weeks of gestation. These medications help accelerate the development of the baby’s lungs and other organs, preparing them for an earlier birth, and reducing the severity of respiratory distress syndrome and other prematurity complications.
In cases of severe or uncontrolled bleeding, or if there are signs of fetal distress, an emergency cesarean section may be performed regardless of gestational age. Otherwise, management focuses on conservative measures to allow the pregnancy to continue as close to term as possible. Patients are advised to seek immediate medical attention for any vaginal bleeding or signs of severe abdominal pain.
Complications and Delivery Planning
Placenta previa carries several potential complications for both the mother and the baby. For the mother, the primary risk is severe hemorrhage, which can occur during pregnancy, labor, or delivery due to the placenta’s abnormal attachment. This excessive bleeding may necessitate blood transfusions and, in rare instances, could lead to an emergency hysterectomy. Another potential maternal complication is placenta accreta spectrum, where the placenta grows too deeply into the uterine wall, making it difficult to detach after birth and increasing the risk of massive hemorrhage.
For the baby, concerns include preterm birth, often a consequence of severe bleeding or early delivery. Preterm babies face risks such as low birth weight, respiratory distress syndrome due to underdeveloped lungs, and other complications requiring neonatal intensive care. Placenta previa can also increase the risk of the baby being in an abnormal position for delivery, such as breech.
A vaginal delivery is generally contraindicated in cases of placenta previa because cervical dilation during labor can cause severe bleeding. Therefore, a planned cesarean section (C-section) is the standard method of delivery for most individuals with placenta previa.
The timing of a planned C-section for uncomplicated placenta previa is typically scheduled between 36 and 37 weeks of gestation to balance the risks of spontaneous bleeding with the benefits of fetal maturity. However, if severe bleeding occurs at any point, an emergency C-section may be performed earlier.