Abnormalities of Placental Implantation

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Chapter 194 Abnormalities of Placental Implantation

INTRODUCTION

Description: Failure of the normal process of decidua formation results in a placental implantation in which the villi adhere directly to (accreta, 78%), invade into (increta, 17%), or go through (percreta, 5%) the myometrium. One portion (partial) or all (total) of the placenta may be involved.
Prevalence: Difficult to assess; estimates vary from 1 in 1667 to 1 in 70,000 pregnancies (average 1 in 7000).
Predominant Age: Reproductive, average 29.
Genetics: No genetic pattern.

ETIOLOGY AND PATHOGENESIS

Causes: Abnormal decidua formation at the time of placental implantation. (Imperfect development of the fibrinoid [Nitabuch’s] layer.) Abnormal site of placental implantation (previa, 64% of placenta accreta, cornual or lower uterine segment, or uterine scars such as site of previous cesarean delivery).
Risk Factors: Placenta previa (without previous uterine surgery 5%, with previous surgery 15% to 70%), previous cesarean delivery, multigravidity (1 of 500,000 for parity <3, 1 of 2500 for parity >6), older pregnant women, previous uterine curettage, previous uterine sepsis, previous manual removal of the placenta, leiomyomata, uterine malformation, prior abortion, endometrial ablation.

CLINICAL CHARACTERISTICS

Signs and Symptoms

• Failure of normal placental separation
• Abnormally heavy bleeding after delivery of the placenta (may be life threatening)
• History of antepartum hemorrhage

DIAGNOSTIC APPROACH

Differential Diagnosis

• Placenta previa
• Uterine rupture with expulsion of the placenta
• Uterine rupture at the time of manual removal of the placenta

Associated Conditions: Placenta previa (15%), postpartum hemorrhage.

Workup and Evaluation

Laboratory: Complete blood count after delivery to assess blood loss (which may be excessive).
Imaging: No imaging indicated. (Ultrasonography has been used to make the diagnosis before labor in unusual cases. 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: None indicated.
Diagnostic Procedures: Generally diagnosed only at delivery by failure of the normal separation mechanism. Final diagnosis is established histologically.

Pathologic Findings

Absence of the decidua basalis (replaced by loose connective tissue). The decidua parietalis may be normal or absent. The villi may be separated from the myometrial cells by a layer of fibrin.

MANAGEMENT AND THERAPY

Nonpharmacologic

General Measures: Aggressive fluid and blood support as necessary. Oxytocin or other uterotonic agents to promote uterine contractions after placental delivery (if accomplished).
Specific Measures: Most patients require hysterectomy. If the invasion of the myometrium is incomplete and the bladder is spared, conservative management by uterine packing may be possible. Any time the diagnosis is considered, preparations for hysterectomy, including anesthesia, instruments, and adequate blood, should be ready before any attempt is made to free the placenta.
Diet: Nothing by mouth until the patient’s condition has been stabilized.
Activity: Bed rest until the patient’s condition has been stabilized.
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

Uterotonics should be available, and broad-spectrum antibiotics should be given prophylactically.

FOLLOW-UP

Patient Monitoring: Hemodynamic monitoring during the acute diagnosis and treatment.
Prevention/Avoidance: Patients at high risk may be studied by ultrasonography in an attempt to identify the absence of the subplacental hypoechoic zone or the presence of lacunar blood-flow patterns. If present, plans for autologous blood donation and elective cesarean hysterectomy may be made. The absence of these findings does not rule out this possibility.
Possible Complications: Life-threatening hemorrhage may occur; maternal mortality of 2% to 6% has been reported for treatment by hysterectomy and up to 30% for conservative management. Coagulopathy secondary to blood loss and replacement is common. Spontaneous rupture of the uterus may occur before labor. Rupture of the uterus or inversion may occur during attempts to remove the placenta.
Expected Outcome: Most patients go to term with normal fetal development. If the possibility is recognized and appropriate treatment is rendered, maternal survival is probable, although loss of the uterus is common. It is hypothesized that small areas of accreta may result in placental cotyledon(s) being torn from the placenta and that these cotyledons may become placental polyps.

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MISCELLANEOUS

ICD-9-CM Codes: 667.0 (All types, without hemorrhage), 666.0 (All types, with hemorrhage).

REFERENCES

Level II

Silver RM, Landon MB, Rouse DJ, et alNational Institute of Child Health, Human Development Maternal-Fetal Medicine Units Network. Maternal morbidity associated with multiple repeat cesarean deliveries. Obstet Gynecol. 2006;107:1226.

Level III

Abbas F, Talati J, Wasti S, et al. Placenta percreta with bladder invasion as a cause of life-threatening hemorrhage. J Urol. 2000;164:1270.

American College of Obstetricians and Gynecologists. Placental pathology. ACOG Committee Opinion 102. Washington, DC: ACOG, 1991.

American College of Obstetricians and Gynecologists. Guidelines for diagnostic imaging during pregnancy. ACOG Committee Opinion 299. Obstet Gynecol. 2004;104:647.

American College of Obstetricians and Gynecologists. Postpartum hemorrhage. ACOG Practice Bulletin 76. Obstet Gynecol. 2006;108:1039.

American College of Obstetricians and Gynecologists. Endometrial ablation: ACOG Practice Bulletin 81. Obstet Gynecol. 2007;109:1233.

Ash A, Smith A, Maxwell D. Caesarean scar pregnancy. BJOG. 2007;114:253.

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

Breen J, Neubecker R, Gregori C, Franklin J. Placenta accreta, increta and percreta. Obstet Gynecol. 1977;49:43.

Clark SL, Koonings PP, Phelan JP. Placenta previa/accreta and prior cesarean section. Obstet Gynecol. 1985;66:89.

Clark SL, Phelan JP, Yeh SY, et al. Hypogastric artery ligation for obstetric hemorrhage. Obstet Gynecol. 1985;66:353.

Cotton DB, Read JA, Paul RH, Quilligan EJ. The conservative aggressive management of placenta previa. Am J Obstet Gynecol. 1980;137:687.

Cox SM, Carpenter RJ, Cotton DB. Placenta percreta: ultrasound diagnosis and conservative surgical management. Obstet Gynecol. 1988;72:452.

Morison JE. Placenta accreta: a clinicopathologic review of 67 cases. Obstet Gynecol Annu. 1978;7:107.

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

Price FV, Resnik E, Heller KA, Christopherson WA. Placenta previa percreta involving the urinary bladder: a report of two cases and review of the literature. Obstet Gynecol. 1991;78:508.

Read JA, Cotton DB, Miller FC. Placenta accreta: changing clinical aspects and outcome. Obstet Gynecol. 1980;56:31.

Teteris NJ, Lina AA, Holaday WJ. Placenta percreta. Obstet Gynecol. 1976;47:15S.

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