Placenta Previa – Causes, Symptoms, Diagnosis, Treatment and Ongoing care
- Placental implantation in the lower uterine segment in advance of presenting fetal part and in proximity to or covering the internal os
- Complete previa: Placenta covers entire internal cervical os.
- Partial previa: Placenta covers part of internal cervical os.
- Marginal previa: No exact definition; commonly means placental edge is adjacent to cervical os by ultrasound but not overlapping.
- Low-lying placenta: Placental edge located in the lower uterine segment but does not encroach on or cover the os; has been defined as within 2–3 cm of cervical os by ultrasound
- System(s) affected: Cardiovascular; Reproductive
- Average gestational age of 1st bleed, 27–36 weeks
- Most common cause of minimally painful bleeding after 20 weeks gestational age
- Approximately 10% of low-lying placentas at 10–20 weeks persist to term.
- Some evidence that shortened cervical length in the 3rd trimester is associated with increased risk of bleeding
- Approximately 0.4% of primiparous pregnancies, with increasing incidence with cesarean deliveries in future pregnancies
- Up to 5% incidence in grand multiparous women
- History of placenta previa (relative risk [RR] = 8.0)
- Advanced maternal age (RR = 9.0 if >40 years of age)
- Multiparity (5% if >5 deliveries) (RR = 1.1–1.7)
- Assisted reproductive technology (RR = 2.0)
- Multiple gestation
- Smoking (RR = 1.4–3)
- Cocaine use
- Male fetus (RR = 1.4)
- Asian (RR = 1.9)
- Previous cesarean deliveries:
- 1 previous C-section: RR = 1.5 (95% confidence interval [CI] 1.3–1.8)
- 2 previous C-sections: RR = 2.0 (95% CI 1.3–3.0)
- 4 previous C-sections: RR = 44.9 (95% CI 13.5–15.0)
- Induced or spontaneous abortion/curettage (Ashermans) (RR = 1.6)
- Leiomyoma or history of lower uterine segment surgery
No genetic links have been identified.
Once pregnancy is diagnosed, risk factors are not modifiable. If patient has any risk factors for previa and anatomic survey is suggestive of previa, serial ultrasounds should be performed for monitoring purposes. Patient should be counselled regarding potential bleeding and should be triaged with all bleeding episodes.
- Invasion of trophoblastic giant cells into the decidua, myometrium, and myometrial spiral arteries
- Increased inflammatory cell infiltration compared with women with normal implantation sites
- As lower uterine segment expands and the trophoblastic tissue expands towards the fundus, many marginal or low-lying placentas will resolve to a safe distance from the cervix to allow vaginal delivery (1).
Prior endometrial insult/injury/scar or other unknown uterine factors as listed previously.
Commonly Associated Conditions
- Abnormal presentations (e.g., oblique and/or transverse fetal lie)
- Antepartum/intrapartum/postpartum hemorrhage
- Small for gestational age or intrauterine growth restriction (up to 16% in some reports after controlling for confounders)
- Vasa previa or velamentous insertion of the cord
- Premature rupture of membranes due to antepartum bleeding
- 5-10% of previas are associated with placenta accreta.
- Placenta accreta encompasses various types of abnormal placentations in which chorionic villi attach directly to or invade the myometrium but do not cross the uterine serosa.
- Placenta accreta affects approximately 1/2,500 pregnancies with increasing prevalence due to increased rates of cesarean section.
- Risk greater with increasing number of cesarean deliveries
- Associated with an increased risk of hemorrhage necessitating cesarean hysterectomy
- Painless bright red vaginal bleeding in 2nd or 3rd trimester (classic presentation)
- Contractions also may be present.
- Decreased fetal movement or nonreassuring fetal heart tracing
- Do not perform digital cervical exam until placental position has been verified in any woman with a complaint of bleeding.
- Careful sterile speculum exam not contraindicated
- Check for vaginal or cervical source of bleeding.
- Check for ferning and Nitrazine testing for rupture of membranes.
- Perform cultures: Gonorrhea, Chlamydia, group B Streptococcus.
Diagnostic Tests & Interpretation
- If patient is Rh-negative, Kleihauer-Betke test for maternal–fetal hemorrhage to determine if Rho(D) immune globulin (RhoGAM) is needed
- Ultrasound to confirm presence of previa
- Rule out accreta, percreta if suspicious findings on ultrasound
- Fetal testing and monitoring during all active bleeding
Initial lab tests
- Maternal blood type and antibody screen
- Complete blood count (CBC): Normocytic, normochromic anemia with acute bleeding
- Prothrombin time (PT)/international normalization ratio (INR), and partial thromboplastin time (PTT): Coagulopathy is rare but may occur.
- Fibrinogen is optional and DIC panel is often inconclusive.
- Kleihauer-Betke test: Positive test indicates fetal–maternal transfusion may be present.
- Cross-match at least 4 units of packed red blood cells if bleeding ≥1 soaked pad/hour
Follow-Up & Special Considerations
Repeat hemoglobin/hematocrit determinations as needed to assess blood loss.
Development of ultrasound, especially the transvaginal scan, has helped in the definitive diagnosis and management of placenta previa (2).
- External abdominal sonography with full, then empty bladder. Full bladder can cause compression of lower uterine segment causing a false appearance of previa.
- Careful assessment may still miss some posterior previas if fetal vertex is low.
- Vaginal probe sonography using 8.4 MHz transducer to further define placental position. Translabial ultrasound may also be utilized but may not be able to specifically discern characteristics of previas.
- Given increased risk of accreta, the placental-uterine interface should be closely examined for evidence of lakes or other abnormal vasculature
- MRI if concerned for placenta accreta without definitive ultrasound diagnosis; important also for surgical planning
Follow-Up & Special Considerations
- Previas found on ultrasound before 35 weeks should have a repeat ultrasound prior to delivery.
- 12% of previas at 10–20 weeks persist until term.
- 62% of previas at 28–31 weeks persist until term.
- 75% of previas at 32–35 weeks persist until term.
- Anterior previas are more likely to resolve than posterior previas since the anterior lower uterine segment expands more quickly.
Placental pathology often shows giant trophoblasts at placental interface, evidence of abruption.
- Abruptio placentae
- Vasa previa
- Vaginal and cervical pathology including erosion, cancer, trauma, or infections
- Oxygen supplementation if needed
- Aggressive IV fluids/blood products as needed: Fresh-frozen plasma, platelets, and packed red blood cells
- Tocolytics for uterine contractions may be used with caution, especially to allow for steroids for fetal lung maturity if possible (3)[A]. Calcium channel blockers such as nifedipine, loading dose of 10 mg p.o. every 20 minutes × 3, then every 4–6 hours:
- Watch for placental hypoperfusion (nonreassuring fetal heart tracing).
- Contraindications: Term fetus or unstable maternal or fetal cardiovascular status
- β-agonists such as terbutaline 0.25 mg SC every 3–4 hours; watch for maternal–fetal tachycardia and maternal hypertension and pulmonary edema.
- Magnesium sulfate 4–6 g IV load over 20 minutes, then 2–3 g/hour continuous infusion (4)[A]; watch for toxicity: loss of reflexes, pulmonary edema, cardiac arrest.
- Nifedipine 10 mg every 20 minutes × 3 doses loading dose and then every 4–8 hours depending on bleeding and contractions. Use dependent on maternal cardiovascular status as cannot administer if hypotensive
- Decrease physical activity to avoid bleeding.
- Avoid vaginal exams, sexual intercourse, douching, or other vaginal manipulation.
- If stable maternal–fetal status, delay delivery until 38 weeks (5)[C].
- Amniocentesis to determine fetal lung maturity for elective delivery <38 weeks
- A trial of labor may be considered with anterior previa >2 cm away from the cervix (6)[B].
- Transfuse platelets at <20,000 (or <50,000–100,000 depending on institutional guidelines prior to surgery).
- Blood volume is increased in pregnancy; patient can lose >30% maternal blood volume before shock develops.
- Central line placement as needed after checking coagulation studies
- With significant hemorrhage, Rh-negative women should receive 300 µg Rho(D) immune globulin (RhoGAM).
Issues for Referral
- Maternal–fetal medicine consult for delivery decisions regarding stable patients
- Neonatal ICU team should be alerted for high-risk delivery and consulted for preterm delivery.
- Appropriate interdisciplinary planning with blood bank, anesthesia, staff regarding plans if massive hemorrhage ensues intraoperatively or if unanticipated accreta encountered
Recombinant factor VII is an alternative blood product for disseminated intravascular coagulopathy when fresh-frozen plasma and cryoprecipitate fail (7)[C].
Cesarean delivery is indicated for partial or complete previa when fetal lung maturity is demonstrated or when patient becomes unstable secondary to blood loss prior to fetal maturity.
- Bed rest and NPO until delivery decision made
- 1 or 2 large-bore IV sites and IV fluids as needed for resuscitation
- Continuous fetal heart and contraction monitoring
- Heavy vaginal bleeding warrants inpatient observation at least until hemodynamically stable.
- 1st bleed usually is self-limited. Patients should be observed and steroids for fetal lung maturity administered. Once stable, preterm patients may be observed on an outpatient basis without difference in outcome (5)[B].
- Multiple large bleeds may necessitate admission until scheduled delivery between 34 and 36 weeks depending on institutional guidelines.
- May consider transfer to high-risk perinatology service based on patient condition, local services, and concern for accreta
- Evidence that shortened cervical length in the 3rd trimester is an independent risk factor for bleeding episodes (8)
Lactated Ringer’s or normal saline solution
- Continuous fetal heart and contraction monitoring
- Frequent vital signs, including fluid intake and output
- Demonstration of fetal well-being by fetal heart tracing or biophysical profile
- Demonstration of maternal hemodynamic stability: No active bleeding for >48 hours
- Proximity of patient to health care facility and patient reliability
- Repeat ultrasound of placenta location if last ultrasound was done at <37 weeks’ gestational age.
- Placentas should be sent for pathologic evaluation.
No restrictions once stable; NPO if delivery possible
- Maternal death is rare with cesarean section (<1%).
- Greatest fetal risk is preterm delivery and consequences of hypoxemia if delay in delivery with fetal tracing abnormalities.
- Perinatal mortality is <10%.
- History of prior cesarean section and/or general anesthesia increases risk of needing a blood transfusion.
- Placenta accreta is associated with increased risk of hemorrhage and need for cesarean hysterectomy.
- Disseminated intravascular coagulation risk is low unless massive bleeding is present. Follow coagulation studies, and replenish FFP and clotting factors as needed.
- Fetal anemia and Rh isoimmunization
1. Predanci M, et al. A sonographic assessment of different patterns of placenta previa ‘migration’ in the third trimester of pregnancy. J Ultrasound Med2005;24:773.
2. Sinha P, Kuruba N. Ante-partum haemorrhage: an update. J Obstet Gynaecol. 2008;28:377–81.
3. Sharma A, Suri V, Gupta I. Tocolytic therapy in conservative management of symptomatic placenta previa. Int J Gynaecol Obstet. 2004;84:109–13.
4. Briggs GG, Wan SR. Drug therapy during labor and delivery, part 2 [Review]. Am J of Health-System Pharm. 2006;63(12):1131–9.
5. Oyelese Y, Smulian JC. Placenta previa, placenta accreta, and vasa previa. Obstet Gynecol. 2006;107:927–41.
6. Bhide A, Prefumo F, Moore J, et al. Placental edge to internal os distance in the late third trimester and mode of delivery in placenta praevia. BJOG.2003;110:860–4.
7. Alfirevic Z, Elbourne D, Pavord S, et al. Use of recombinant activated factor VII in primary postpartum hemorrhage: the Northern European registry 2000–2004. Obstet Gynecol. 2007;110:1270–8.
8. Stafford IA, Dashe JS, Shivvers SA, et al. Ultrasonographic cervical length and risk of hemorrhage in pregnancies with placenta previa. Obstet Gynecol.2010;116:595–600.
See Also (Topic, Algorithm, Electronic Media Element)
- 641.03 Placenta previa without hemorrhage, antepartum
- 641.13 Hemorrhage from placenta previa, antepartum
36813001 placenta previa (disorder)
- Placenta previa is a major cause of antepartum bleeding in the 2nd and 3rd trimesters.
- Do not perform digital cervical exam, only careful speculum exam.
- Ultrasound, both transvaginal and transabdominal, is used to verify placenta location and diagnosis.
- Delivery is by cesarean section with rare exceptions.