Author:
W. BrysonBendall
KatherineHiller
Description
- Placental tissue overlying or proximate to the internal cervical os
- Uterine enlargement and cervical dilation cause placental vessels near the cervix to tear, resulting in vaginal bleeding
- >90% of placenta previa diagnosed before 20 wk will migrate and have normal placental location at term
- Causes 20% of all antepartum hemorrhage
- Classification:
- Placenta previa: The internal cervical os is covered completely or partially by the placenta (previously referred to as total or partial previa, respectively)
- Low-lying placenta: The placenta is implanted in the lower uterine segment and the edge does not reach the internal os and remains outside a 2-cm wide perimeter
Etiology
- Incidence: 3-5/1,000 births
- Maternal mortality: 0.03%
- Perinatal morbidity and mortality: Triple, due to preterm delivery
- Factors affecting location of implantation:
- Increased number of curettages from spontaneous or induced abortions
- Abnormal endometrial vascularization
- Delayed ovulation
- Risk factors:
- Multiparity (5% grand multiparous patients vs. 0.2% nulliparous)
- Multiple gestation (risk in twin pregnancy increases 30-40%)
- Prior C-section (up to 3× increase, increases with number of prior C-sections)
- Increased maternal age (0.1% age 12-19 yr, 0.9% age ≥35 yr)
- Previous placenta previa (4-8% recurrence)
- Smoking (2-4 times increase)
- Male fetus (14% increase)
- Assisted fertilization
- Associated conditions:
- Placenta accreta, increta, percreta (growth of placenta into uterine wall) occur in 5-10% of patients with placenta previa; sustained bleeding may require C-section hysterectomy
- Preterm premature rupture of membranes
- Amniotic fluid embolism; associated with pathologies of the placenta
- Vasa previa: Fetal vessels course through membranes and cover os
- Congenital anomalies
- Abnormal fetal presentation
- Higher risk for massive bleeding
- Short uterine cervical length in the third trimester
- Sinus venosus at margin of placenta
- Advanced maternal age at time of C-section
- Prior C-section
Signs and Symptoms
- Painlessvaginal bleeding in pregnancy after 20 wk is placenta previa until proven otherwise
- Caution: It may present with pain if the patient is also in labor
History
- Painless bright red vaginal bleeding in 70-90%
- Uterine contraction in 20% first episode of bleeding typically occurs at 27-32 wk
- Bleeding may range from minor to massive; number of bleeding episodes does not correlate with degree of placenta previa
- Inciting factors - usually none; recent intercourse or heavy exercise may contribute
- Initial bleeding is often self-limited and not lethal, but often recurs
- Common incidental finding on US in second trimester (6% at 16-18 wk)
Physical Exam
- Never do a digital exam or instrument probe of the cervix in second-trimester vaginal bleeding until placenta previa has been ruled out
- Hypotension and tachycardia may indicate hemorrhagic shock
- Fetal heart tones and maternal contractions should be monitored along with other vital signs
Essential Workup
Ultrasonography is the diagnostic procedure of choice
Diagnostic Tests & Interpretation
Lab
- CBC
- Type and screen; upgrade to cross-match if transfusion is indicated
- Rh status
- If coagulopathy suspected (rare): Prothrombin time/partial thromboplastin time, fibrin-split products, fibrinogen (<300 mg/dL is abnormal)
Imaging
- Transabdominal US: 93-98% accurate:
- Drain bladder prior to performing
- False negative: Obesity, posterior or lateral placenta, fetal head over cervical os
- False positive: Overdistended bladder
- Transvaginal US: Safe and most accurate:
- More accurate than transabdominal
- Does not exacerbate bleeding when performed properly
- Considered the gold stand ard
- Color-flow Doppler US: Used to determine placenta accreta
- MRI: Not used in an emergent situation to confirm this diagnosis:
- May be useful on an outpatient basis in evaluating placental abnormalities such as accreta and percreta
Differential Diagnosis
- Placenta abruption (may occur concurrently)
- Uterine rupture
- Fetal vessel rupture
- Cervical/vaginal trauma
- Cervical/vaginal lesions
- Bleeding disorder
- Spontaneous abortion
- “Bloody show” of term or preterm labor
Prehospital
- Patient with vaginal bleeding at >24 wk should be transported to a facility that can hand le high risk and premature delivery
- Place patient in left lateral recumbent position if hypotensive in second half of pregnancy
- O2, cardiac monitor, and 2 large-bore IVs, and begin infusion of IV crystalloid
- If the patient is bleeding profusely, specialists (OB, surgery, blood bank, etc.) should be mobilized early
Initial Stabilization/Therapy
- Resuscitation for hemorrhagic shock as with any source, including FFP if coagulopathy
- ABCs + FHT monitoring (<120 or >160 is abnormal)
- 2 large-bore IVs with normal saline (NS) or lactated Ringer (LR) for resuscitation
- Left lateral recumbent position if hypotensive in second half of pregnancy
- Emergent OB consultation for patients with active bleeding
ED Treatment/Procedures
- Immediate OB consultation
- Blood transfusion to keep Hct >30
- RhoGAM if mother is Rh negative
- Fetal monitoring
- Keep NPO and on bed rest until considered stable by OB
- Magnesium sulfate used in consultation with OB for its neuroprotective effects in patients who may need a preterm C-section
- Antenatal steroids (betamethasone) at 24-34 wk to stimulate prenatal lung maturity
- Emergency C-section or delivery for continued bleeding or fetal compromise
Medication
- RhoGAM: 1 vial (300 mcg) IM if not already given at 28 wk; may need >1 vial if KB indicates >15 mL of fetal RBS
- Magnesium sulfate: 6 g IV over 20 min, then 2-4 g/hr; adjust to contractions
- Betamethasone: 12 mg IM q24h × 2 doses
Disposition
Admission Criteria
Active bleeding in placental previa is a potential obstetric emergency, and all patients should have OB consultation and be admitted for monitoring and treatment
Discharge Criteria
Select patients may be managed on outpatient basis following consultation with OB, if bleeding is resolved
Follow-up Recommendations
- Asymptomatic patients
- Bed rest is not necessary
- Avoid strenuous physical activity
- Pelvic rest (no intercourse or tampons in vagina) if placenta previa found after 28 wk or at any time if associated with bleeding
- Report bleeding or contractions
- If <32 wk and placenta previa or low-lying placenta is found, repeat formal US and follow up with OB should be scheduled at 32 wk
- 70% of patients will have a second episode of bleeding
- CunninghamFG, LevenoKJ, BloomSL, et al. Williams' Obstetrics. 24th ed.New York: McGraw-Hill; 2014.
- DynaMed. Placenta previa . 2009. Available at http://www.DynamicMedical.com.
- HackerNF, GamboneJC, HobelCJ. Hacker and Moore's Essentials of Obstetrics and Gynecology. 6th ed.Philadelphia, PA: Elsevier Inc.; 2016.
- HasegawaJ, NakamuraM, HamadaS, et al. Prediction of hemorrhage in placenta previa . Taiwan J Obstet Gynecol. 2012;51:3-6.
- HockbergerRS, WallsRM, Gausche-HillM. Rosen's Emergency Medicine: Concepts and Clinical Practice. 9th ed.Philadelphia, PA: Elsevier; 2018.
- LockwoodCJ, Russo-StieglitzK. Placenta previa: Epidemiology, clinical features, diagnosis, morbidity and mortality . UpToDate. Available at http://www.uptodate.com.
- ScottJR, GibbsRS, KarlanBY, et al. Danforth's Obstetrics and Gynecology. 10th ed.Philadelphia, PA: Lippincott Williams & Wilkins; 2008.
- SilverRM. Abnormal placentation: Placenta previa, vasa previa and placenta accreta . Obstet Gynecol. 2015;126:654-658.
See Also (Topic, Algorithm, Electronic Media Element)
Placental Abruption