Schedule | Lectures | Seminars | Tests | Glossary | Cases | Index | Review  | Search | Feedback
Human Reproduction Logo

SEMINAR 3 :   PREGNANCY INDUCED HYPERTENSION AND OBSTETRICAL HEMORRHAGE
A.  A1.  A2.  A3.  A4.  B.  B1.  B2. 

Case Histories- Third Trimester Bleeding : Placenta Previa

Placenta previa is one cause of significant third trimester bleeding in which placental implantation in the lower uterine segment at the internal cervical os. The incidence of placenta previa is 1 in 200 pregnancies.

Variable degrees of placenta previa are described, as follows:

total : the placenta totally covers the internal cervical os.


Schematic of complete placenta previa
Click here for a larger view.
Schematic of complete placenta previa. The placenta completely covers the internal os of the cervix.
Credits: C. Matthew Peterson, M.D

Placenta accreta in uterine specimen
Click here for a larger view.
Placenta accreta in uterine specimen. Placenta accreta or percreta may be associated with placenta previa especially if the patient has had a previous cesarean section.
Credits: Steven L. Clark, M.D.

partial: the placenta partially covers the internal cervical os


Partial placenta previa
Click here for a larger view.
Partial placenta previa. The placenta partially covers the internal os.
Credits: Steven L. Clark, M.D.

marginal: the edge of the placenta extends to the margin of the internal cervical os


low lying posterior placenta previa :the placenta is within reach of the examining finger introduced through the cervix.


Low lying  posterior placenta
Click here for a larger view.
Low lying posterior placenta.
Credits: C. Matthew Peterson, M.D.

low lying placenta

Placenta previa presents in a characteristic fashion. Typical historical findings are: painless bleeding after 20 weeks, and bleeding which is often heavy and episodic. Coagulopathies are relatively rare with this entity.

The following groups are at special risk for placenta previa:


  • Multiparous patients
  • Advanced maternal age (over 40)
  • Previous cesarean sections
  • Large placenta ( includes multiple gestation)
  • Induced abortion

Typically, placenta previa is a painless experience for the patient. The uterus is usually soft and is not tender to palpation. A pelvic examination is not performed, because of the risk of increasing the hemorrhage by digital disruption of the placenta at the cervical os. The diagnosis is confirmed by ultrasound.

If the initial episode of bleeding subsides, hospitalization of the patient with placenta previa is appropriate. Typically the patient will remain at bedrest, in an attempt to delay a repeat bleeding episode. Transfusions are utilized to keep the hematocrit above 25%. Cesarean delivery is deferred until the fetus is mature, or until dangerous bleeding develops. Cross matched blood is maintained in the blood bank for emergency use. Corticosteroids are given to induce fetal lung maturity, and reduce the risk of fetal intraventricular hemorrhage if the pregnancy is less than 34 weeks gestation. Placenta accreta or percreta may be associated with placenta previa especially if the patient has had a previous cesarean section.

Your next patient is a 25 year old cocaine addict at 29 weeks who presents with accute onset of severe uterine tenderness and moderate vaginal bleeding. You might expect to find all of the following except:


Click on your choice:
 A. intrauterine fetal demise

 B. placental abruption

 C. disseminated intravascular coagulation

 D. uterine rupture


top