What is Placenta Previa?
Placenta previa is a condition where the placenta (the organ that provides nutrients to the baby in the womb) covers part or the entire opening inside the neck of the womb (the cervix). This can lead to severe bleeding after birth, posing a risk to both the mother and the baby. As a result, the baby often needs to be delivered by cesarean section (surgical operation to deliver the baby) as delivering the natural way won’t be safe.
Most cases of placenta previa are caught early in the pregnancy through ultrasound scans. However, it may also come to light if a pregnant woman goes to the emergency room with painless bleeding during the second or third trimester of her pregnancy. Having placenta previa also increases the risk of developing conditions collectively known as placenta accreta spectrum (PAS) which includes placenta accreta, increta, and percreta. These conditions occur when the placenta grows too deeply into the uterine wall.
Excessive bleeding after birth, from placenta previa or PAS, can become uncontrolled and may require a blood transfusion, or even a hysterectomy (surgical removal of the uterus). A hysterectomy ends a woman’s ability to have future pregnancies. In extreme cases, it may require hospitalization in an intensive care unit (ICU) or, unfortunately, it can lead to death.
What Causes Placenta Previa?
The exact cause of placenta previa, a condition where the placenta covers the cervix, isn’t known. However, it’s linked with scarring and damage in the uterus lining also known as the endometrium. Some sets of people are more likely to develop placenta previa. This includes: older mothers, women who have had many pregnancies, smokers, cocaine users, those who’ve previously undergone a certain type of surgery (known as suction and curettage), individuals who’ve used assisted reproductive technology, those with a history of cesarean sections, and those who’ve had placenta previa before.
Here’s a simple explanation of how the placenta forms: When a sperm fertilizes an egg, it creates a “fertilized egg” or zygote. For this zygote to grow, it needs an environment rich with oxygen and collagen, which is a kind of protein. The zygote starts dividing and develops an outer layer of cells called the blastocyst. The cells of the blastocyst, the trophoblast, eventually form the placenta and the fetal membranes.
These trophoblast cells stick to the lining of the uterus (called the “decidua basalis”) and create a normal pregnancy. But, if there is an old scar on the uterus, it could provide a similar environment rich in oxygen and collagen. The trophoblast may stick onto this scar instead, leading to the placenta developing over the cervical opening. This or the placenta burrowing into the walls of the uterus muscle (myometrium) can cause placenta previa.
Risk Factors and Frequency for Placenta Previa
Placenta previa, a condition affecting pregnancies, is found in approximately 0.3% to 2% of cases during the third trimester. This condition has become more apparent due to the increasing number of cesarean sections being performed.
Signs and Symptoms of Placenta Previa
Placenta previa is a condition that can occur during pregnancy. Certain factors can increase the risk of developing this condition, including being older than 35 years, having multiple previous pregnancies, smoking, using certain drugs like cocaine, having a history of curettage (a procedure to remove tissue from inside the uterus), and having one or more cesarean sections in the past. It is important to note that being older might also be associated with a greater number of pregnancies and a higher likelihood of uterine procedures or fertility treatments, which could also contribute to placenta previa. Additionally, harmful substances found in cigarettes such as nicotine and carbon monoxide can cause the blood vessels in the placenta to narrow, disrupting the blood flow and leading to abnormal placement of the placenta.
Typically, the main symptom of placenta previa is painless bleeding from the vagina during the second or third trimester of pregnancy. This bleeding can sometimes occur after sexual intercourse, vaginal examinations, or labor, while in some cases, there may not be an apparent cause. During an examination with a speculum (a medical tool used to examine the vagina and cervix), the bleeding could range from minimal to active, and in cases where the cervix is dilated, the placenta may be visible. However, doctors avoid carrying out a digital examination (using a finger to feel inside the vagina) as it could lead to severe bleeding.
Testing for Placenta Previa
Regular ultrasound scans during the first and second trimester of pregnancy can help detect placenta previa—an abnormal placement of placenta—early. If it’s found early, there’s a good chance it’ll improve by the time of delivery, thanks to the natural movement of the placenta. In fact, this applies to about 90% of “low-lying” placentas, which means it’s close to or covering the cervix. Doctors often suggest a follow-up ultrasound between 28 to 32 weeks into the pregnancy to check if the placenta previa still exists.
If a pregnant woman experiences vaginal bleeding in the second or third trimester, a transabdominal ultrasound (an ultrasound through the abdomen) can be performed before any physical examination. If placenta previa is suspected, a transvaginal ultrasound (an ultrasound through the vagina) may be done to confirm the placenta’s location. This particular method has proven to be more reliable than a transabdominal ultrasound and is considered safe.
The presence of Placenta Accreta Spectrum (PAS) also needs to be checked. Under normal circumstances, the placenta attaches to the uterus’s wall, but in PAS, it attaches too deeply and invades the muscle of the uterus. In severe cases, the placenta may penetrate the uterus and affect other organs. This condition can sometimes cause severe bleeding during delivery, and therefore, it’s important to identify this early for proper planning. Ultrasound is highly effective in diagnosing PAS. In certain cases, when the placenta previa is at the back of the uterus or if there’s a chance it might invade the bladder, an MRI might be helpful. However, MRIs are expensive and haven’t been proven to give better diagnosis or result than an ultrasound. If PAS is likely, your doctor might discuss planning a c-section and potentially removing the uterus to prevent severe bleeding during delivery. This procedure involves leaving the placenta in place.
Treatment Options for Placenta Previa
If diagnosed with a condition called placenta previa, where the placenta is blocking the cervix, a patient is typically scheduled for a C-section or cesarean section, a surgical procedure to deliver the baby, around 36 to 37 weeks of their pregnancy. However, if any complications arise, the C-section may need to be performed earlier.
If a patient with placenta previa experiences vaginal bleeding, they should receive immediate medical attention, which may entail tracking the baby’s heart rate and placing intravenous lines (tubes used to administer medications or fluids). If the bleeding is substantial, the patient may need to receive a blood transfusion.
If the patient experiences severe or consistent bleeding, they may require a C-section, no matter how far along they are in their pregnancy. If the bleeding stops, it’s possible to wait and see, as long as the pregnancy isn’t past 36 weeks. Once they reach 36 weeks, a C-section is generally recommended. In such circumstances, patients may be admitted to the hospital and given particular medications to protect the baby’s brain and help their lungs mature. Even if the bleeding stops for over 48 hours and the baby is in good health, the patient may still need to stay in the hospital or continue being monitored at home, depending on different factors like the stability of the patient, the number of bleeding episodes, their proximity to the hospital, and their ability to follow medical advice.
When it comes to the planned C-section, it’s important for it to occur under controlled conditions. All medical professionals involved, such as the surgeon, anesthesiologist, and pediatricians, should be adequately informed. The patient may need to have intravenous lines set up and have blood prepared for a potential transfusion. Anesthesiologists generally recommend regional anesthesia, which numbs certain areas of the body, over general anesthesia, which makes the patient unconscious, as it has been shown to lessen blood loss and the need for blood transfusion. If a postpartum hemorrhage (excessive bleeding after childbirth) occurs, there are various measures that can control it.
During the C-section, the surgeon usually makes a vertical incision for the best access. The baby is delivered first, then the placenta detaches and the uterine incision can be closed. However, there may be blood loss related to the placenta detachment, which can be managed via different methods. If bleeding cannot be controlled, a hysterectomy, a surgery to remove the uterus, may be necessary.
For patients who wish to maintain their fertility after being diagnosed with placenta accreta, a serious pregnancy condition where the placenta grows too deeply into the uterine wall, there’s the choice of conservative management. This approach leaves the placenta in place until it naturally loses its blood supply, making it safer for the remaining placental tissue to be removed or reabsorbed. While this approach can preserve future fertility, it carries a risk of recurrent placenta accreta and ongoing bleeding that may necessitate a delayed hysterectomy.
Lastly, for patients with a low-lying placenta, where the placenta is close but not covering the cervix, they may be able to proceed with a natural delivery but should be prepared for the potential need for a C-section and more risk for excessive bleeding after delivery. There’s no universally agreed-upon approach for a related condition called marginal placenta previa, and the most appropriate method depends on various factors.
What else can Placenta Previa be?
During pregnancy, vaginal bleeding can be caused by many different things. The reason for the bleeding can change depending on what stage of the pregnancy a women is in. In the first and second trimester, bleeding could be due to a number of conditions, including:
- subchorionic hematoma
- cervicitis
- cervical cancer
- threat of a miscarriage
- ectopic pregnancy
- molar pregnancy
In the third trimester, bleeding may happen due to:
- labor
- placental abruption (premature separation of the placenta from the womb)
- vasa previa (overtopping of the lower part of the womb with fetal blood vessels)
- placenta previa (placenta covering the womb’s opening)
Among these, placental abruption is very serious as it might threaten the lives of the mother and the baby. This condition is identified by severe belly pain, bleeding, and irregular fetal heartbeat. It happens in about 1% of births and can cause serious illness and possible death due to bleeding.
Vasa previa is not common, occurring in around 1 in 2500 to 1 in 5000 pregnancies. If the fetal blood vessels, which run over the internal cervical os, tear due to the rupture of the membranes, it could lead to severe bleeding in the fetus or newborn.
What to expect with Placenta Previa
In the case of newborns, there’s usually a three to four times increase in the risk of neonatal death and health complications due to placenta previa, mainly because of preterm delivery. Placenta previa is a condition where the placenta, which is the organ that provides oxygen and nutrients to the baby, covers the mother’s cervix. This condition raises risks for the newborn such as preterm birth, lower birth weight, lower APGAR scores (a quick test performed on a baby at 1 and 5 minutes after birth to determine how well the baby is doing outside the womb), and increased chances of respiratory distress syndrome (a breathing disorder in newborns).
On the other hand, about 90% of placenta previa cases in mothers are resolved through delivery. However, it’s been found that women with anterior placentas (where the placenta is attached to the front wall of the womb) tend to experience poorer health outcomes. These women are more likely to lose a significant amount of blood and have higher rates of hysterectomy (a surgical procedure to remove the uterus) compared to other placental locations. This is because the placenta can attach to a previous uterine incision, causing what is known as Placenta Accreta Spectrum (PAS). PAS is a condition where the placenta grows deeply into the uterine wall and an unplanned incision may cut through the placenta. Women with confirmed placenta previa may face the risk of needing a blood transfusion, injury to nearby organs, cesarean hysterectomy, admission to intensive care, and at worst, death. There is also an increased risk in their subsequent pregnancies.
Possible Complications When Diagnosed with Placenta Previa
Placenta previa, when not detected and managed effectively, can cause substantial issues in pregnancy, affecting both the mother and baby. One significant repercussion is vaginal bleeding after the birth, known as postpartum hemorrhage. This intense blood loss, defined as losing a liter or more of blood within the 24 hours post-delivery, could result in various serious medical conditions. These might include blood transfusion, uterine muscle contraction drugs (uterotonics), procedures to block the uterine artery (embolization) or the iliac artery, balloon tamponade to control bleeding, or even complete removal of the uterus (hysterectomy). Furthermore, intense infections or even death can occur.
In addition, placenta previa is linked to premature birth, low weight at birth, lower APGAR scores (which assess a newborn’s health), extended hospital stays, and rising instances of blood transfusion.
Complications from Placenta Previa:
- Vaginal bleeding
- Postpartum hemorrhage
- Blood transfusion
- Hysterectomy
- Admission to intensive care
- Severe infections
- Potential death
- Preterm birth
- Low birth weight
- Lower APGAR scores
- Extended hospital stay
- Greater instances of blood transfusion
It’s also worth noting that women with a history of previous C-sections and placenta previa are at higher risk for Placenta Accreta Syndrome (PAS). The risk for this condition, where the placenta attaches to the uterus more deeply than normal, increases with each successive cesarean surgery, with risks of 3%, 11%, 40%, 61%, and 67% for the first, second, third, fourth, and fifth (or more) C-section, respectively.
Preventing Placenta Previa
Placenta previa is a condition where the placenta, which provides nourishment to the baby, blocks the opening to the birth canal, the cervix. This makes it unsafe to deliver the baby normally through the vagina.
In cases where there are no complications, babies in this situation are usually delivered via cesarean section (a surgical procedure to deliver the baby), when the pregnancy reaches between 36 to 37 full weeks.
Resting in bed, avoiding sexual activity, and not having internal physical examinations are advised for pregnant women diagnosed with placenta previa. This is because any touching or manipulation of the placenta can cause severe bleeding.
If a pregnant woman with placenta previa experiences any episodes of vaginal bleeding, it is important to get to the emergency room as soon as possible.
Having placenta previa before, or having had a cesarean section in the past, might increase a woman’s chance of developing placenta accreta. Placenta accreta is a serious condition where the placenta attaches too deeply into the uterine wall.
If there is any suspicion of placenta accreta, increta, or percreta (variations of the condition where the placenta becomes deeply embedded into or even through the uterus), the doctor might need to perform a cesarean hysterectomy. This is a surgical procedure that involves delivering the baby via cesarean section and removing the uterus.
