What is placenta previa?
The placenta is what nourishes and protects your baby in utero, filtering out what she doesn’t need and delivering the oxygen and nutrients she does. Most of the time, it attaches to the top or side of the uterus. But when the placenta implants low in your uterus, part of it can cover the cervix — a condition known as placenta previa.
There are several types of previa:
- Complete previa: The placenta covers the entire cervical opening
- Partial previa: The placenta covers part of the cervical opening
- Marginal previa: The placenta borders the cervix
No matter what kind of previa it is, the placenta physically blocks the opening to the birth canal (a.k.a. the vagina) — your baby's way out come his or her big B-day.
How common is placenta previa?
If you’re diagnosed with the condition before 28 weeks, don’t worry: As many as 15 percent of women are diagnosed with some degree of placenta previa during the second trimester, usually during a routine ultrasound. But because the uterus grows at such an accelerated rate in early pregnancy, the majority of these cases — 90 percent, thankfully — resolve, meaning the placenta moves up and away from the cervix before week 30 of pregnancy. (In fact, your practitioner may not even mention a possible previa to you until your third trimester, since the odds are it won’t persist until then.) In fact, only about one of every 150 to 300 expecting women is diagnosed with placenta previa during the third trimester, when the placenta is unlikely to budge.
A number of conditions put you at greater risk of placenta previa, including:
- Advanced maternal age. Placenta previa is three times more likely to occur in women over the age of 30 than those under the age of 20.
- Second or later pregnancy. The condition is more common in women who have had at least one other pregnancy.
- Multiples. Being pregnant with two or more babies increases your likelihood of placenta previa.
- Abnormalities of the uterus. Women who have naturally abnormally- shaped uteruses or have scarring on their uterine lining due to uterine surgeries, including C-sections and D&C procedures, are also at higher risk.
- Smoking. Cigarette use during pregnancy increases your chances of developing a host of complications including placenta previa.
Symptoms and diagnosis
Placenta previa is most commonly discovered and diagnosed not on the basis of symptoms but during a routine second-trimester ultrasound (though there isn't even the potential for problems with a previa until the third trimester). But sometimes the condition announces itself in the third trimester (occasionally earlier) with the following symptoms:
- Bleeding. The changing shape of your uterus during the third trimester can destabilize the connection between your uterus and placenta if it is low-lying, causing bleeding. Placenta previa is, in fact, considered the most common cause of abnormal bleeding in the latter part of pregnancy. It's estimated that 70 to 80 percent of women with the condition experience some bright-red bleeding (not just vaginal spotting, which is typically normal) sometime after the week 20 — though it happens most frequently between weeks 34 and 38.
- Cramping. While it’s not common to feel pain, some women do experience cramping.
- Breech position. Your baby is more likely to be in a breech position when you have placenta previa. That’s because in a typical pregnancy, the most comfortable third-trimester position for a baby is head down at the bottom of the uterus, where there’s the most room. But with a previa, the placenta occupies that space where your baby’s head would normally gravitate, causing her to stay in (or move to) a breech position.
What happens if you bleed
Many bleeding incidents can be treated effectively before blood loss puts you or your baby at risk. However severe bleeding may be cause for an immediate delivery. If premature labor seems imminent, you may receive steroid shots to mature your baby's lungs more rapidly before a C-section is performed. Likewise, if bleeding occurs after 36 weeks, your practitioner may also advise an immediate C-section. In very rare cases, heavy bleeding may require a blood transfusion.
Prevention and treatment
While there’s no way to prevent placenta previa, once you’ve been diagnosed and have reached your third trimester your health care provider may recommend measures to ensure a safe pregnancy and delivery, especially if you experience any bleeding. These might include:
- Pelvic rest. This means abstaining from intercourse, discontinuing any use of tampons or vaginal douches, and foregoing pelvic exams.
- Increased fetal monitoring. Your doctor may want to keep an eye on your baby to make sure his heartbeat remains strong and his movements are consistent.
- Hospital care. Although studies have not shown bed rest has clear benefits for women with placenta previa, your practitioner may want you to remain at a hospital until your delivery, particularly if you’ve had a bleeding incident, in order to monitor you and your baby continuously.
You'll also want to keep a lookout for signs of preterm labor, which is more common with placenta previa.
Labor and delivery
About 75 percent of women with placenta previa in the third trimester deliver via C-section before labor starts. Although women with a marginal previa can sometimes deliver vaginally, nearly all partial and complete placenta previas require a C-section to avoid severe, life-threatening bleeding.
What you need to know
Unfortunately a placenta previa diagnosis during the third trimester means that you may not realize your ideal birth plan. And a previa-induced bleeding incident, if you experience one, can be frightening. But since you’ll be on vigilant lookout for symptoms and you know to seek immediate treatment if you bleed, you and your baby will be OK. The most important thing to keep in mind: The vast majority of women with placenta previa safely deliver healthy babies.
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