Pocket ObGyn – Placental Abruption / Placenta Previa / Vasa Previa / Placenta Accreta
See Abbreviations
Definition and Epidemiology (Am J Epidemiol 2001;153:332)
- Decidual hemorrhage causing premature separation of the placenta
- Incid: 1/120 pregnancies. w/ PPROM (2–5%)
Pathophysiology
- Decidual hemorrhage ® decidual cells release tissue factor ® thrombin (uterotonic) is formed, up-regulates apoptosis, induces expression of inflamm cytokines ® tissue necrosis (Am J Obstet Gynecol 2004;191:1996)
Etiology
- Mechanical force (trauma) or abn uteroplacental vessels (constriction from vascular dz such as smoking or hypertensive dz)
- Acute: High pres arterial bleeding
- Chronic: Low pres venous hemorrhage, often due to inflamm necrosis
- Factors a/w abruption: Smoking, cocaine use, mat vascular dz, prolonged ruptured membranes, abruption in prior Preg, uterine leiomyoma, multiparity, advanced mat age, HTN
Clinical Manifestation and Physical Exam
- Acute: Vaginal bleeding, abdominal/back pain, contractions (high frequency, low amplitude), abdominal/uterine tenderness, bright red bld in vaginal vault
- Chronic: Intermittent vaginal bleeding, often in small amounts, dark/old bld in vagina
- Couvelaire uterus: Purple tinged uterus due to bld in myometrium seen at cesarean
- Placenta: Gross retroplacental clots & histologic decidual necrosis or placental infarction
Diagnostic Workup/Studies
- Clinical dx by Hx, exam, sono, & suspicion
- Continuous electronic fetal monitoring & uterine tocometry: Frequent uterine contractions (tetany) & nonreassuring fetal heart tracing
- US: 25–50% sens
Retroplacental clot: Elevated region of placenta less echogenic than placental tissue ® if seen, likelihood of abruption HIGH
Subchorionic clot: Elevated highly echogenic region of membrane Thickened placenta that moves w/ mat mvmt
- Labs: CBC, T&C, coags, Kleihauer–Betke (trauma, Rh-mother)
early mat serum AFP: 10´ risk of abruption if AFP not a/w a fetal anomaly (Prenat Diagn 2007;27:240)
¯ fibrinogen (<200 mg/dL) = most sensitive lab predictor for sev abruption
DIC commonly seen w/ abruption
Treatment and Medications
- Large bore IV placement & fluid/bld resusc as necessary
- Term or near term: If nonreassuring fetal heart tones ® emergent CS
- Preterm: Generally delay deliv if fetal well-being is reassuring Many chronic abruptions will not require deliv
Antenatal steroids if deliv anticipated prior to 34 w gest Tocolysis not used in women w/ acute abruption
Antenatal testing & serial growth ultrasounds w/ expectant mgmt Be prepared w/ uterotonics in the postpartum period
Placenta Previa
Definition and Epidemiology
- Placenta overlying or proximate to internal cervical os (definitions have varied)
Complete: Placenta completely covers os (>20–30%)
Partial: Placental edge partially covers os
Marginal: Placental edge w/i 2 cm of the internal os but does NOT cover os
Low-lying placenta: Placental edge extends into lower uterine segment
- Incid: 4% of pregnancies over 20 w (J Matern Fetal Neonatal Med 2003;13:175)
- w/ increasing parity, cigarette smoking, h/o placenta previa, prior uterine Surg, & prior CD
1–4% in the Preg following a CD Up to 10% if ³4 CDs
Etiology
- Trophoblastic implantation: Scarred endometrium may this process
- Increased need for placental oxygen or nutrient deliv (smokers, multi gest, higher altitude residence)
- risk of previa at earlier gestational age as the unidirectional growth of trophoblastic tissue toward fundus (trophotropism) is Lower uterine segment w/ gestational age ® Over 90% of placenta previa identified in the 2nd trimester resolve at term
Clinical Manifestation and Physical Exam
- Painless vaginal bleeding in the 2nd & 3rd trimesters
- DO NOT perform digital cervical exam on a pt suspected to have a previa
- A sterile speculum exam is used to visually assess cervical dilation
Diagnostic Workup/Studies
- Identification of placenta during routine US, usually performed from 18–22 w
- If concern for previa ® rpt US to assess extent of previa or verify resolution
- Prior CSs + previa = look carefully for evid of placenta accreta (below)
Treatment and Medications
- Pelvic rest (no intercourse or digital exams for duration of Preg)
- Outpt mgmt: Small bleeds resolved for >7 d, live close to the hospital, & are highly compliant
- Inpt mgmt: Actively bleeding placenta previa, ³2 episodes of vaginal bleeding If pt can be stabilized & deliv is not needed immediately for fetal distress:
Large-bore IV access
Baseline labs (H/H, platelet count, type & screen, coags) Antenatal steroids should be administered <34 w gest
- CD at 36–37 w gest (Obstet Gynecol 2011;118:326)
Vasa Previa
Definition and Epidemiology (Ultrasound Obstet Gynecol 2001:109)
- Umbilical vessels cross internal cervical os in front of fetal presenting part
- Prevalence: 1:2500 deliveries (OBG Survey 2004:245)
- Type 1: From a velamentous cord insertion (vessels not surrounded by Wharton’s jelly)
- Type 2: From vessels btw lobes of a bilobed or succenturiate lobed placenta
Clinical Manifestation
- Vaginal bleeding w/ rupture of membranes ® fetal vessel laceration
- Sinusoidal fetal HR (indicating fetal anemia)
Diagnostic Workup/Studies
- Transvaginal US w/ color Dopplers to diagnose before labor
- Once identified, continue to monit w/ US throughout Preg
15% resolve (Obstet Gynecol 2000;95:572)
Begin NSTs twice weekly from 28–30 w to evaluate for cord compression
- Apt test: Qualitative test on vaginal bleeding + fetal bld = indicative of vasa previa Negative = mat bld, no ruptured vasa Rarely used test in clinical practice.
Treatment and Medications
- Highly consider administration of antenatal corticosteroids prior to 34 w gest CD pior to rupture of Suggested gestational age: 34–36 w.
- Pelvic rest (no intercourse or digital exams for duration of Preg)
Placenta Accreta
Definition and Epidemiology
- Abn placental implantation: Placental villi attach to the myometrium or grow through it instead of being contained by decidual cells
- Risk of accreta w/ placenta previa & increasing number of CDs (Obstet Gynecol 2006;107:1226)
| CS and risk for placenta accreta | ||
| # of prior CDs | Risk w/ no placenta previa | Risk w/ placenta previa |
| 0 | Minimal | 1–5% |
| 1 | 0.3% | 11–25% |
| 2 | 0.6% | 35–47% |
| 3 | 2.4% | 40% |
| ³4 | Not given | 50–67% |
Pathology
- Accreta: Chorionic villi attached to myometrium
- Increta: Chorionic villi invade the myometrium just up to the serosa
- Percreta: Chorionic villi protrude through the uterine serosa
Risk Factors
- Advanced mat age, smoking, advanced parity, submucosal fibroids, Asherman’s syn
- Most strongly correlated w/ placenta previa + prior uterine incision (eg, CD, myomectomy)
Clinical Manifestation
- Given US advancements, often diagnosed prior to clinical presentation
- Placenta does not detach after deliv ®
Diagnostic Workup/Studies
- Women w/ placenta previa or low lying anter placenta & prior uterine Surg ® sono for accreta at 20–24 w
- Ultrasonographic findings suggestive of placenta accreta:
Loss of hypoechoic boundary btw placenta & bladder or thin myometrium <1 mm Placental lacunae w/ turbulent flow
Irreg bladder wall w/ extensive vascularity Loss of retroplacental clear space
- Consider color Doppler sono, 3D sono, & Cystoscopy if bladder invasion suspected
Subsequent Workup
- If accreta identified, pt should be seen by a team of physicians (Anesthesia, General Surg, Interventional Radiology, Uro) to prepare for cesarean hysterectomy
- Monit closely for vaginal bleeding & abdominal pain throughout Preg
Treatment and Medications
- CD at 34–36 w, be prepared for hysterectomy (Obstet Gynecol 2011;118:323)
- Steroids for fetal lung maturity if deliv prior to 34 w gest
- PPH w/ extreme bld loss Maintain IV access & T&C for bld products. Consider internal iliac artery balloon catheters, postsurgical embolization. See Chap. 16 for massive xfusion protocol & bld products.