Placenta Previa

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Chapter 216 Placenta Previa

INTRODUCTION

Description: Placenta previa is implantation of the placenta in a location that leaves part or all of the cervical os covered. This is associated with potentially catastrophic maternal bleeding and obstruction of the uterine outlet. Several degrees are recognized: total, partial, marginal, and low-lying placenta. These degrees may vary with cervical dilation or gestational age.

Prevalence: Seen in 0.3% to 0.5% of deliveries.

Predominant Age: Reproductive, average age 29 years.

Genetics: No genetic pattern.

ETIOLOGY AND PATHOGENESIS

Causes: Implantation by the zygote low in the uterine cavity (in close proximity to the cervical os). Defective decidual vascularization, resulting from inflammation or atrophy, has been implicated.

Risk Factors: Multiparity, advanced maternal age (>35: 1% of deliveries, >40: 2%), prior cesarean delivery (two to five times increase), induced abortion, smoking (2-fold increase), cocaine use, multiple gestation, high altitude, and prior abortion.

CLINICAL CHARACTERISTICS

Signs and Symptoms

• Painless vaginal bleeding (70%, generally not present until late second or early third trimester); may be catastrophic in amount, although initial episodes are rarely fatal; blood is maternal in origin

• Uterine hyperactivity possibly present with bleeding (20%)

• Heavy or prolonged bleeding after delivery

DIAGNOSTIC APPROACH

Differential Diagnosis

• Bloody show of early labor

• Placental abruption

• Vasa previa

• Low-lying placenta

Associated Conditions: Placenta accreta (15% to 25% of patients), increta, or percreta and prematurity.

Workup and Evaluation

Laboratory: Complete blood count, type and cross-match blood products for possible replacement.

Imaging: Ultrasonography (transabdominal) to determine placental location and condition, fetal status. (False-positive ultrasonographic results may occur with a full bladder; suspicious studies should be repeated with the bladder empty. Low-lying placentas noted in studies performed at less than 30 weeks may “migrate,” leaving the cervix free at term [up to 90% of cases].)

Special Tests: Kleihauer-Betke test for fetal–maternal transfusion, clot tube to assess possibility of coagulopathy, Apt test to identify fetal blood loss (such as from a vasa previa).

Diagnostic Procedures: History, ultrasonography. (Pelvic examination is contraindicated until the location of the placenta can be ascertained.)

Pathologic Findings

Placental implantation in the lower uterine segment.

MANAGEMENT AND THERAPY

Nonpharmacologic

General Measures: Evaluation, hemodynamic stabilization, fetal assessment. If placenta previa is suspected, no vaginal examinations until the location and degree of placental obstruction can be determined.

Specific Measures: If bleeding is heavy or the placenta obstructs delivery, cesarean delivery is indicated. Marginal (low-lying) placental implantation may be managed conservatively if it occurs long before term. Bleeding from the placental site may be heavy, requiring extensive measures (including hysterectomy, hypogastric artery ligation or embolization) to control bleeding.

Diet: No specific dietary changes indicated unless active bleeding is present or the patient’s condition is unstable.

Activity: Bed rest is generally indicated.

Patient Education: American College of Obstetricians and Gynecologists Patient Education Pamphlet AP038 (Bleeding During Pregnancy), AP006 (Cesarean Birth), AP025 (Ultrasound Exams).

Drug(s) of Choice

Fluid and blood product replacement as needed. Steroid therapy to accelerate fetal lung maturation has been advocated for patients remote from term. Oxytocin, methylergonovine maleate (Methergine), and prostaglandin (E₂) therapy to assist with uterine contraction after delivery. Rh (D) immune globulin should be given as indicated in mothers who are Rh negative. If tocolysis is required, MgSO4 is preferred.

Contraindications: Beta mimetic agents should not be used if there is significant maternal blood loss or hypotension.

FOLLOW-UP

Patient Monitoring: Normal health maintenance.

Prevention/Avoidance: None.

Possible Complications: Catastrophic maternal hemorrhage, fetal anoxia. Coagulation defects may occur as a result of heavy or prolonged blood loss. Significant bleeding from the placental site may result in maternal compromise, and extensive measures (including hysterectomy) to achieve control must be taken. Preterm delivery represents the greatest source of morbidity for the fetus. Roughly 35% of infants whose mothers require transfusion require transfusion themselves.

Expected Outcome: Generally good—25% to 30% of patients complete 36 weeks of gestation despite labor or repetitive bleeding.

MISCELLANEOUS

ICD-9-CM Code: 641.1.

Cobo E, Conde-Agudelo A, Delgado J, et al. Cervical cerclage: an alternative for the management of placenta previa? Am J Obstet Gynecol. 1998;179:122.

Wing DA, Paul RH, Millar LK. Management of the symptomatic placenta previa: a randomized, controlled trial of inpatient versus outpatient expectant management. Am J Obstet Gynecol. 1996;175:806.

Ananth CV, Smulian JC, Vintzileos AM. The association of placenta previa with history of cesarean delivery and abortion: a metaanalysis. Am J Obstet Gynecol. 1997;177:1071.

Besinger RE, Moniak CW, Paskiewicz LS, et al. The effect of tocolytic use in the management of symptomatic placenta previa. Am J Obstet Gynecol. 1995;172:1770.

Joshi VM, Otiv SR, Majumder R, et al. Internal iliac artery ligation for arresting postpartum haemorrhage. BJOG. 2007;114:356. Epub 2007 Jan 22

Rouse DJ, MacPherson C, Landon M, et alNational Institute of Child Health, Human Development Maternal-Fetal Medicine Units Network. Blood transfusion and cesarean delivery. Obstet Gynecol. 2006;108:891.

Taipale P, Hiilesmaa V, Ylostalo P. Diagnosis of placenta previa by transvaginal sonographic screening at 12–16 weeks in a nonselected population. Obstet Gynecol. 1997;89:364.

American College of Obstetricians and Gynecologists. Ultrasonography in pregnancy. ACOG Practice Bulletin 58. Obstet Gynecol. 2004;104:1449.

Booher D, Little B. Vaginal hemorrhage in pregnancy. N Engl J Med. 1974;290:611.

Chamberlain G. ABC of antenatal care. Antepartum haemorrhage. BMJ. 1991;302:1526.

Chamberlain G, Steer P. ABC of labour care: Obstetric emergencies. BMJ. 1999;318:1342.

Oyelese Y, Smulian JC. Placenta previa, placenta accreta, and vasa previa. Obstet Gynecol. 2006;107:927.

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