Placenta Previa

Symptoms

• Painless, bright red vaginal bleeding, typically occurring after 20 weeks of gestation, often in the late second or early third trimester.
• Bleeding that may be initially light and then stop, only to recur days or weeks later, often with increasing severity.
• Bleeding associated with uterine contractions or cramping (less common).
• Profuse, active vaginal bleeding (emergency symptom).
• Signs of maternal hemodynamic instability, such as a rapid heart rate, low blood pressure, lightheadedness, or paleness (emergency symptom).
• Fetal distress on monitoring, such as abnormal heart rate patterns (emergency symptom).

Causes & Risk Factors

• The exact cause of placenta previa is unknown.
• A leading theory suggests that conditions causing scarring or damage to the upper uterine lining (endometrium), such as from previous cesarean deliveries, dilation and curettage (D&C), or myomectomy, may encourage the placenta to implant in the less-scarred lower uterine segment.
• Another theory proposes that a larger placental surface area, as seen in multiple gestations (e.g., twins), increases the chance of the placenta covering or encroaching upon the cervical opening.
• Previous cesarean delivery (risk increases with the number of prior cesarean deliveries).
• Previous placenta previa (recurrence rate is 4-8%).
• Advanced maternal age (over 35 years).
• Multiparity (having had multiple previous pregnancies).
• Multiple gestation (e.g., twins, triplets).
• Prior uterine surgery (e.g., myomectomy, dilation and curettage [D&C]).
• Maternal smoking.
• Cocaine use during pregnancy.
• Assisted reproductive technology (ART), such as in vitro fertilization (IVF) (possible risk factor).
• Male fetus (possible risk factor).

Diagnosis

• Review of obstetric history for risk factors like prior cesarean deliveries or previous placenta previa.
• Inquiry about the onset, amount, color, and character of any vaginal bleeding, and any associated pain or contractions.
• Abdominal examination, where the uterus is typically soft, non-tender, and consistent with gestational age.
• Transvaginal Ultrasound (TVS), which is the gold standard for accurately locating the placenta and measuring its distance from the internal cervical os. This method is safe and highly accurate.
• Transabdominal Ultrasound (TAS), often used for initial screening. If a low-lying placenta is suspected on TAS, it should be confirmed with TVS.
• Magnetic Resonance Imaging (MRI), which is not routinely used for placenta previa diagnosis but may be used to evaluate for suspected co-existing placenta accreta spectrum (PAS).
• Diagnosis of placenta previa is made when ultrasound shows the placental tissue covering any part of the internal cervical os after 20 weeks of gestation.
• Diagnosis of a low-lying placenta is made when the placental edge is within 20 mm (2 cm) of the internal os but not covering it.
• A diagnosis made in the second trimester requires follow-up imaging in the third trimester (typically around 32 weeks) to see if the placenta has moved away from the cervix.
• Differential diagnosis includes placental abruption, vasa previa, uterine rupture, local causes of bleeding (e.g., cervicitis, cervical polyps, cervical cancer), and labor ('bloody show').
• Digital vaginal examination is strictly contraindicated as it can provoke severe bleeding.
• Speculum examination may be performed cautiously to rule out local causes of bleeding, but only in a setting where immediate cesarean delivery is possible.

Treatment Options

• Pelvic rest, which includes avoiding sexual intercourse, douching, and digital vaginal exams.
• Activity restriction, often involving avoiding strenuous activity, heavy lifting, and prolonged standing, though strict bed rest has limited evidence.
• Outpatient management for stable, asymptomatic women who can quickly access hospital care; hospitalization is recommended for active bleeding or other risk factors.
• Serial ultrasounds to monitor the placenta's location.
• Antenatal corticosteroids (e.g., betamethasone) for fetal lung maturation between 24 and 34 weeks of gestation for women at risk of preterm delivery.
• Tocolytics, which may be used cautiously and for a short duration (e.g., 48 hours) to prolong pregnancy to allow for corticosteroid administration, though their use is individualized.
• Rh(D) immune globulin administered to Rh-negative women after any episode of vaginal bleeding.
• Iron supplementation to treat or prevent anemia due to blood loss.
• Cesarean delivery, which is the required mode of delivery for placenta previa at or near term.
• Timing of elective cesarean delivery for uncomplicated placenta previa is typically recommended between 36+0 and 37+6 weeks of gestation, though it may be earlier depending on bleeding severity, maternal stability, and fetal status.
• Regional anesthesia (spinal or epidural) is generally preferred for cesarean delivery unless there is severe maternal hemorrhage or fetal compromise.
• Immediate hospitalization for any significant bleeding.
• Maternal stabilization, including intravenous access with large-bore catheters, fluid resuscitation, and blood product transfusion (packed red blood cells, platelets, fresh frozen plasma) as per massive transfusion protocols.
• Emergency cesarean delivery for life-threatening maternal hemorrhage or non-reassuring fetal status, regardless of gestational age.
• Referral to a tertiary care center with a Level III/IV NICU, 24-hour blood bank, and experienced obstetric, anesthesia, and surgical teams for management and delivery.

Frequently Asked Questions