Placenta Previa in Pregnancy

Picture of a fetus attached to the wall of the uterus. The cause of placenta previa is due to the location of the placenta in the uterus.

Placenta previa is a complication of pregnancy in which the placenta (the organ that joins the mother and fetus and transfers oxygen and nutrients to the fetus) is implanted either near to or overlying the outlet of the uterus (womb). Placenta previa is found in approximately four out of every 1000 pregnancies beyond the 20th week of gestation.

• The main symptom of placenta previa is vaginal bleeding.
• Several terms have been used to characterize placenta previa.
• Types of placenta previa, for example:
  • Complete
  • Partial
  • Marginal
  • Low
  • Anterior
  • Posterior

• Vaginal bleeding after the 20th week of gestation is the primary sign of placenta previa.
• The bleeding usually is painless.
• Some women may have abdominal pain during uterine contractions.

Bleeding occurs at some time in most women with placenta previa, and it is the primary sign after the 20th week during pregnancy. Pain from placenta previa can range from mild to severe. The bleeding is typically painless; however, in some pregnant women, it can be associated with uterine contractions and abdominal pain.

Placenta previa symptoms can be associated with other complications of pregnancy.

• Placenta accreta occurs when the placenta actually grows into the wall of the uterus, attaching to the muscle layer and resulting in difficulty separating the placenta from the wall of the uterus at delivery. This complication can cause life-threatening bleeding and commonly requires hysterectomy at the same time as the Cesarean section. Placenta accrete occurs in 5% to 10% of women with placenta previa.
• Preterm premature rupture of the membranes (PPROM) can result from the bleeding associated with placenta previa.
• Other abnormalities of the placenta or umbilical cord can be associated with placenta previa
• Breech or abnormal presentation of the fetus can be associated with placenta previa due to the inability of the fetal head to enter the lower part of the uterus.
• Decreased fetal growth rate (intrauterine fetal growth restriction) is possible.
• Emotional disturbances are related to the anxiety created by the woman knowing that she has placenta previa.

1. Complete placenta previa refers to the situation in which the placenta completely covers the opening from the womb to the cervix.
2. Partial placenta previa refers to the placenta that partially covers the cervical opening (since the cervical opening is not dilated until time for delivery approaches, bleeding may occur after the cervix has begun to dilate).
3. Marginal placenta previa refers to a placenta that is located adjacent to, but not covering, the cervical opening.
4. Low-lying placenta or low placenta has been used to refer both to placenta previa and marginal placenta previa.
5. Anterior and posterior placenta previa are sometimes used after ultrasound examination is preformed to further delineate the exact position of the placenta within the uterine cavity.

• A number of factors can increase the likelihood that the placenta will be located in the lower part of the womb and potentially cover the cervical opening.
• Scar tissue in the upper regions of the uterus can promote the growth of the placenta in the relatively unscarred lower segment of the uterus. Scarring of the tissues in the upper uterus can be a result in:
  • Prior Cesarean deliveries (placenta previa occurs in 10% of women who have had four or more Cesarean deliveries)
  • Prior D&C procedures (curettages) for miscarriages or induced abortions
  • Any surgery or instrumentation of the uterine cavity
• In some women, placenta previa occurs because the placenta grows larger to compensate for decreased function (lowered ability to deliver oxygen and/or nutrients to the fetus) or a need for greater function. This need for a larger placental area can increase a woman's risk of developing placenta previa. for example:
  • Multiple gestations (twins, triplets, etc.)
  • Cigarette smoking
  • Living at a high altitude
• The risk of having placenta previa also increases with increasing maternal age and with the number of previous births.
• Women who have had placenta previa in one pregnancy are at greater risk for this complication in subsequent pregnancies.
• Asian women have a slightly increased risk of placenta previa than women of other races, although the reason for this is unclear.
• Women carrying male fetuses are slightly more likely to have placenta previa than women with female fetuses.
• Since the placenta normally migrates away from the cervical opening as pregnancy progresses, women in the earlier stages of pregnancy are more likely to have placenta previa than are women at term.
• Some women between 10 and 20 weeks gestation will have some evidence of placenta previa on ultrasound examination, but most of these cases resolve on their own as the pregnancy progresses.

The bleeding of placenta previa typically begins after the 20th week of gestation. A woman should always seek medical care if she experiences bleeding in the later stages of pregnancy.

Placenta previa is suspected when a woman in the 20th week of gestation or later reports having bleeding.

• An ultrasound examination (see below) is used to establish the diagnosis. The ultrasound examination is performed before a physical examination of the pelvis because the physical examination may promote increased bleeding.

Both transabdominal (using a probe on the abdominal wall) and transvaginal (with a probe inserted inside the vagina but away from the cervical opening) ultrasound evaluations may be performed, to determine the exact location of the placenta.

• Women with placenta previa in the 3rd trimester of pregnancy are typically counseled to avoid sexual intercourse and exercise, as well as to reduce their activity level.
• Modified bed rest is generally advised.
• If there has been little or no bleeding, or if the bleeding has stopped, bed rest at home may be prescribed.
• Women who have placenta previa and remain at home must be able to access medical care immediately should bleeding resume, and home care is not appropriate in all cases, for example, if the woman lives far from the hospital.
• Women with larger volumes of bleeding or continuous bleeding require admission to the hospital.
• It is very important to follow the recommendations of your doctor or midwife in this regard.

• Admittance to the hospital is necessary if a pregnant woman is actively bleeding. 
• Treatment of placenta previa depends on the volume of bleeding, the gestational age and condition of the fetus, the position of the placenta and fetus, and whether the bleeding has diminished or is continuing.
• Cesarean delivery ((C-section) may be required for all types of placenta previa and is universally necessary in the case of complete placenta previa.
• Women who are on bed rest at home should follow their doctor's instructions in regard to activity level and follow-up examinations. Follow-up care with your OB/GYN is necessary after you deliver the baby.

• Women with placenta previa who experience heavy bleeding may require blood transfusions in order to replace lost blood.
• Usually, intravenous (IV) fluids are given.
• If the woman has contractions, tocolytic drugs (medications that slow down or inhibit labor) are used, for example, magnesium sulfate and terbutaline (Brethine).
• A woman with placenta previa may be given corticosteroid medications to accelerate fetal lung maturity (when the infant is premature) prior to Cesarean delivery (C-section).

• Cesarean delivery is usually planned for women with placenta previa as soon as the baby can be safely delivered (typically after 36 weeks gestation).
• An emergency Cesarean section or a Cesarean delivery at an earlier gestational age may be necessary for heavy bleeding that cannot be stopped or for fetal distress.

Placenta previa is almost always associated with the need for Cesarean delivery. If there is complete placenta previa, a C-section will be required. Most women with other variations of placenta previa will also require Cesarean delivery.

The vast majority of women with placenta previa in developed countries go on to deliver healthy babies, and the maternal mortality (death) rate is less than 1%. In developing countries where medical resources may be lacking, the risks for mother and fetus are much higher.

• Placenta previa usually cannot be prevented. In some cases, risk factors can be eliminated (such as smoking cessation).
• Bleeding from placenta previa can be reduced in many cases by bed rest, limitation of activity, and/or avoiding sexual intercourse.