Placenta Previa: Types & Risk Factors

• Placenta previa is defined as a placenta that covers the internal cervical os, either partially or completely

Types of Placenta Previa

• Complete previa: The placenta completely covers the internal cervical os
• Partial previa: The placenta partially covers the internal cervical os
• Marginal previa: The edge of the placenta is at the margin of the internal cervical os
• Low-lying placenta: The placenta is implanted in the lower uterine segment, close to the internal cervical os, but does not cover it

Risk Factors

• Previous placenta previa: Women who have had a placenta previa in a previous pregnancy are at higher risk
• Previous cesarean delivery: The risk increases with the number of cesarean deliveries
• Multiple gestation: Carrying twins or more increases the risk
• Advanced maternal age: Women over 35 are at higher risk
• Multiparity: Having had multiple pregnancies increases the risk
• Smoking: Smoking during pregnancy is associated with an increased risk
• Cocaine use: Cocaine use during pregnancy is associated with an increased risk
• In vitro fertilization (IVF): Pregnancies conceived through IVF have a higher risk
• Prior uterine surgery: History of uterine surgeries such as dilation and curettage (D&C) or myomectomy
• Short interpregnancy interval: Pregnancies occurring shortly after a previous pregnancy

Symptoms

• Painless vaginal bleeding is the most common symptom
• The bleeding is often bright red and can range from light to heavy
• Bleeding may occur spontaneously, often in the late second or early third trimester
• Uterine contractions may accompany the bleeding in some cases
• In some cases, placenta previa may be diagnosed during a routine ultrasound without any bleeding

Diagnosis

• Transabdominal Ultrasound: Initial method for assessing placental location; non-invasive
• Transvaginal Ultrasound: Offers a more detailed view of the relationship between the placenta and the cervical os; considered more accurate
• MRI: Used in rare cases when ultrasound findings are inconclusive; helpful in cases of posterior placenta previa

Complications

• Maternal hemorrhage: Significant blood loss requiring blood transfusions and potentially leading to hypovolemic shock
• Preterm labor and delivery: Placenta previa is associated with an increased risk of preterm labor and delivery, leading to neonatal complications
• Placenta accreta spectrum (PAS): Increased risk of placenta accreta, increta, or percreta, where the placenta abnormally attaches to or invades the uterine wall
• Emergency hysterectomy: May be necessary in cases of severe bleeding or placenta accreta
• Maternal anemia: Chronic blood loss can lead to iron deficiency anemia
• Blood transfusion complications: Risks associated with blood transfusions, such as transfusion reactions or infections
• Maternal death: Rare but possible in cases of severe hemorrhage
• Fetal growth restriction: Reduced blood flow to the fetus can result in fetal growth restriction
• Prematurity-related complications: Increased risk of respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, and sepsis in premature infants
• Fetal anemia: Blood loss can lead to fetal anemia
• Stillbirth: In rare cases, severe bleeding can lead to fetal demise

Management

• Initial Assessment: Confirm the diagnosis with ultrasound, evaluate bleeding severity, assess maternal and fetal well-being
• Hospitalization: Recommended for women with placenta previa experiencing bleeding episodes
• Bed Rest: Reduce physical activity to minimize bleeding risk
• Pelvic Rest: Avoid sexual intercourse and vaginal examinations
• Tocolytic Medications: May be used to suppress preterm labor contractions
• Corticosteroids: Administered to accelerate fetal lung maturity if preterm delivery is anticipated (typically between 24 and 34 weeks)
• Magnesium Sulfate: May be administered for neuroprotection of the fetus if delivery is anticipated before 32 weeks
• Blood Transfusion: Administered if significant maternal blood loss occurs
• Anti-D Immunoglobulin: Administered to Rh-negative women to prevent Rh sensitization
• Scheduled Cesarean Delivery: Typically planned at 36-37 weeks gestation to avoid labor and potential hemorrhage

Delivery Considerations

• Cesarean Delivery: Preferred method of delivery for placenta previa to avoid maternal hemorrhage
• Timing of Delivery: Usually scheduled at 36-37 weeks gestation, but may be earlier depending on bleeding episodes
• Anesthesia: Choice depends on maternal and fetal condition; epidural or general anesthesia may be used
• Uterotonic Medications: Administered after delivery to contract the uterus and reduce bleeding risk
• Cell Saver Technology: May be used to collect and re-infuse the patient's own blood during cesarean delivery to minimize the need for allogeneic blood transfusion
• Postpartum Monitoring: Close monitoring for postpartum hemorrhage and anemia

Placenta Accreta Spectrum (PAS)

• Placenta Accreta: Placenta attaches too deeply into the uterine wall but does not penetrate the myometrium
• Placenta Increta: Placenta invades into the myometrium
• Placenta Percreta: Placenta penetrates through the myometrium and may invade adjacent organs

Management of PAS

• Prenatal Diagnosis: Ultrasound and MRI can help identify PAS
• Multidisciplinary Team: Involves obstetricians, maternal-fetal medicine specialists, gynecologic oncologists, interventional radiologists, and neonatologists
• Delivery Planning: Scheduled cesarean hysterectomy is often planned at 34-35 weeks gestation
• Uterine Artery Embolization: May be used to reduce blood flow to the uterus during surgery
• Hysterectomy: Often performed to remove the uterus and placenta en bloc to prevent hemorrhage
• Conservative Management: In rare cases, the placenta is left in situ to resorb, but this is associated with significant risks of hemorrhage and infection

Placenta previa occurs when the placenta covers the internal cervical os, fully or partially. Types include complete, partial, marginal, and low-lying. Risk factors involve previous placenta previa or cesarean delivery, multiple gestation, advanced maternal age, multiparity, and smoking.