Why does placenta previa cause preterm labor
The placenta nourishes and protects your baby throughout pregnancy, filtering out what she doesn’t need and delivering the oxygen and nutrients she does. Show
Most of the time, it attaches to the upper part of the uterus. But if it settles in the lower part of the uterus, you might be diagnosed with placenta previa, or your doctor might say you have a low-lying placenta. What is placenta previa?Placenta previa is a relatively rare pregnancy complication in which the placenta implants low in the uterus and covers part or all of the cervix. Currently, placenta previa is defined as any instance where the placenta covers part or all of the cervix. Previous categories of the condition, including marginal previa (when the placenta is within 2 centimeters of the cervix but doesn't physically cover it), partial previa (when the placenta covers part of the cervical opening) and complete previa (when the placenta covers the entire cervical opening) are no longer used. Instead, in all cases of previa, the placenta physically blocks the opening to the birth canal (the vagina) in some way. That can cause bleeding during pregnancy and labor, and may affect how your baby comes into the world when it's time to deliver. What’s a low-lying placenta and does it mean I'll have placenta previa?A placenta that is close to but not covering the cervical opening (usually within 2 centimeters) is called a low-lying placenta. During the second trimester of pregnancy, often during your 20-week anatomy scan, your doctor may tell you that you have this condition. In roughly 9 out of 10 cases, a low-lying placenta resolves on its own and won’t be considered placenta previa by the time you give birth. As the uterus grows in the third trimester, the placenta will “migrate” on its own, moving up and away from the cervix. Continue Reading Below More About the Placenta and Umbilical CordIf your doctor sees that you have a low-lying placenta in the first or second trimester, he or she will recommend a follow-up ultrasound between weeks 28 and 32 of pregnancy to check the location of the placenta. How common is placenta previa?Placenta previa occurs in about 1 out of every 200 deliveries. If you’re told you have a low-lying placenta or placenta previa before 28 weeks, try not to worry. Many women are diagnosed with placenta previa in the second trimester, usually during a routine ultrasound. The majority of cases of placenta previa that are diagnosed in the first two trimesters resolve by the third trimester, meaning that the placenta moves up and away from the cervix before delivery. In fact, your practitioner may not even mention a possible previa to you until your third trimester, since the odds are that it won’t persist until then. Who is most at risk of placenta previa?Placenta previa risk factors include:
What are the symptoms of placenta previa?Placenta previa or a low-lying placenta is usually discovered and diagnosed not on the basis of symptoms but during a routine second-trimester ultrasound. Sometimes the condition announces itself in the third trimester and occasionally earlier with the following symptoms:
How can I stop bleeding from placenta previa?As your cervix begins to dilate and efface in preparation for birth, there may be tearing in the blood vessels that connect the placenta to the uterus in the area over the cervix. This may cause bleeding. The risk of bleeding increases if more of the placenta covers the cervix. There’s no way to prevent placenta previa, and no surgical or medical procedure can correct the condition. However many bleeding incidents can be treated effectively before blood loss puts you or your baby at risk. Managing light bleeding usually includes avoiding activities that can cause bleeding, like exercise and sex. Severe and uncontrolled bleeding, especially if your baby is in distress, may be cause for an immediate delivery. Head to the emergency room right away if you experience heavy bleeding. How is placenta previa treated?If you’re diagnosed with placenta previa, you'll want to keep a lookout for heavy bleeding as well as signs of preterm labor, which is more common with placenta previa. Your doctor’s goal is to get you as close to your due date as possible. Once you’ve reached your third trimester, your health care provider may recommend measures to ensure a safe pregnancy and delivery, especially if you experience bleeding. These might include:
Can you deliver naturally with placenta previa?It’s sometimes possible to have a vaginal delivery with placenta previa, but most women deliver via C-section to avoid potentially life-threatening bleeding. If you have complete or partial covering of the cervix in the third trimester, you will deliver via C-section, and about 75 percent will be scheduled C-sections before labor starts. If the placenta previa resolves and your placenta doesn’t cover the cervix, you may be able to have a vaginal delivery. If you haven’t yet reached 37 weeks of pregnancy and preterm delivery is necessary, you’ll receive steroid shots to rapidly mature your baby's lungs before a C-section is performed. If severe bleeding occurs after 36 weeks, your practitioner may recommend an immediate cesarean. Other placenta previa complicationsA placenta previa diagnosis during the third trimester means that your practitioner may not be able to stick to your birth plan. And a previa-induced bleeding incident, if you experience one, can be frightening. While placenta previa itself isn’t dangerous for you or your baby, it can lead to serious bleeding and preterm birth. Your doctor will monitor you closely and take precautions to prevent complications. Possible complications of placenta previa include:
Since you’ll be on vigilant lookout for symptoms and you know to seek immediate treatment if you bleed, you and your baby should be okay. The most important thing to keep in mind: The vast majority of women with low-lying placenta or placenta previa safely deliver healthy babies. From the What to Expect editorial team and Heidi Murkoff, author of What to Expect When You're Expecting. What to Expect follows strict reporting guidelines and uses only credible sources, such as peer-reviewed studies, academic research institutions and highly respected health organizations. Learn how we keep our content accurate and up-to-date by reading our medical review and editorial policy. Was this article helpful? Does placenta previa affect labor?If you have placenta previa, when the cervix begins to thin out (efface) and open up (dilate), blood vessels connecting the placenta to the uterus may tear. This can cause severe bleeding during labor and birth, putting you and your baby in danger.
Does low lying placenta cause preterm labor?Possible complications of placenta previa include: Preterm birth. Placenta previa increases the risk of your baby being born before her due date. Preterm delivery, in turn, is linked to babies having a lower birth weight and lower APGAR scores.
How placenta previa cause fetal distress?The neonatal outcomes of placenta previa patients are closely related to the amount of bleeding. Vaginal bleeding during pregnancy leads to insufficient blood supply to the fetus, resulting in fetal growth retardation intrauterine distress.
What is the most common complication of placenta previa?What are possible complications of placenta previa? The greatest risk of placenta previa is too much bleeding (hemorrhage). Bleeding often happens as the lower part of the uterus thins during the third trimester of pregnancy. This causes the area of the placenta over the cervix to bleed.
|