PLACENTA PREVIA

abnormal location of the placenta at or near the internal cervical os 1/200 at time of delivery many are low lying in early pregnancy...

1. abnormal location of the placenta at or near the internal cervical os
2. 1/200 at time of delivery
3. many are low lying in early pregnancy but due to development of lower uterine segment appear to "move upward" as pregnancy nears term
4. 95% of previas diagnosed in T2 resolve by T3; repeat U/S at 30-32 weeks GA

Classification

• Total : placenta completely covers the internal os
• Partial : placenta partially covers the internal os
• Marginal : placenta reaches margin but does not cover any part of the intemal os
• Low lying (NOT a previa) : placenta in lower segment but clear of os,can also bleed, usually later (i.e. in labour)

Etiology

unknown but many associated conditions and risk factors

1. multiparity
2. multiple pregnancy
3. increased maternal ageterine scar due to previous abortion, C-section, D&C, myomectomy
4. uterine tumour (e.g. fibroids) or other uterine anomalies
5. history of placenta previa (4-8% recurrence risk)

Fetal Complications

1. perinatal mortality low but still higher than with a normal pregnancy
2. prematurity (bleeding often dictates early C/S)
3. intrauterine hypoxia (acute or IUGR)
4. fetal malpresentation
5. PPROM
6. risk of fetal blood loss from placenta, especially if incised during C/S

Maternal Complications

1. < 1% maternal mortality
2. hemorrhage and hypovolemic shock
3. anemia
4. acute renal failure
5. pituitary necrosis (Sheehan syndrome)
6. PPH (because lower uterine segment is atonic)
7. hysterectomy
8. placenta accreta

Clinical Features

1. recurrent, PAINLESS bright red vaginal bleeding
   • onset of bleeding depends on degree of previa (i.e. complete bleed earlier)
   • mean GA is 30 weeks; one third present before
   • initially, bleeding may be minimal and cease spontaneously but can be catastrophic later
   • bleeding at onset of labour can occur with marginal placenta previa
2. uterus soft and non-tender
3. presenting part high or displaced
4. diagnosed by U/S (95% accuracy with transabdominal)

Management

1. maternal stabilization; large bore IV with hydration
2. electronic fetal monitoring
3. maternal monitoring
   • vitals, urine output, blood loss
   • bloodwork including hematocrit, CBC, PTT/PT, platelets,fibrinogen, FDP, type and cross match
4. when fetal and maternal condition permit, perform careful U/S examination to determine fetal viability, gestational age and placental status/position
5. Rhogam given if mother is Rh negative
6. management decision depends on
   • previa characteristics (amount of bleeding, degree of previa)
   • fetal condition (GA, level of distress, presentation)
   • uterine activity
7. expectant management and observation of mother and fetus if the initial bleeding episode is slight and GA < 37 weeks
   • admit to hospital
   • limited physical activity
   • no douches, enemas, or sexual intercourse
   • consider corticosteriods for fetal lung maturity
   • delivery when fetus is mature or hemorrhage dictates 
8. delivery if bleeding is profuse, GA > 36 weeks, or L/S ratio is 2:1 or greater
9. usually C-section (incision site dictated by location of previa)