1. PLACENTA PREVIA
Lin Qi De

2. Definition
Placenta previa: Abnormal location of the placenta over ,or in close proximity to the internal os.
Incidence: approximately 1 /250 pregnancy
　　　nulliparas: 1/1000~1/1500 pregnancy
　　grandmultiparas: 1/20

3. Classification
Complete (total) placenta previa: entire cervical os is covered
Partial placenta previa:the margin of the placenta extends across but not all of the internal os.
Marginal:edge of the placenta lies adjacent to the internal os
Low lying placenta:placenta is located near but not directly adjacent to the internal os.

4. Etiology Mechanism: abnormal vascularization Predisposing factors:
Twin pregnancy
Increasing maternal age
Increasing parity
Previous cesarean section

5. diagnosis Painless vaginal bleed: Ultrasonography:
first bleeding episode is 29~30 weeks
Ultrasonography:
benefit in localizing the placenta and diagnosis placenta previa
Bleeding is caused by seperation of part of the placenta from the lower uterine segment and cervix,possibly in response to mild uterine contractions.
If the placenta lies in the posterior portion of the lower uterine segment,its exact relation with the internal os may be more difficult to ascertain. In these instances,transvaginal ultrasonography is useful adjunct to the transabdominal approach.

6. Caution Double setup vaginal examination
No digital vaginal or rectal examination is preformed in case of placenta previa . Only as a final and definitive event and only under conditions of double set up.
This procedure involves careful evaluation of the cervix in the operation room with full preparations for rapid cesarean section.
Before the widespread use of ultrasound, this procedure was done more frequently than it is in modern obstetrics.

7. Management Basic management
Initial hospitalization with hemodynamic stabilization
Enforced bed rest
Restrictions of activity

8. Expectant management (allow for further fetal growth and maturation)
Blood transfusion is given as necessary
Amniocentesis for fetal lung maturity testing
Cesarean birth if fetus is thought to be mature
If the fetus is thought to be mature by gestational age criteria or by amniocentesis for fetal lung maturity testing,there is little benefit to be gained by a delay in delivery.
The degree of bleeding and the maturity of the fetus must be constantly weighted in managing these patients.

9. Indication of vaginal delivery
Delivery can be accomplished with minimal blood loss
Fetus is dead
Major fetal malformation

10. Complication Placenta previa accreta Postpartum hemopphage
Increasing maternal mortality and perinatal mortality