How often do you bleed with placenta previa?

How often do you bleed with placenta previa?

The placenta goes before the fetus into the birth canal. In obstetrics, placenta previa describes a placenta that is implanted somewhere in the lower uterine segment, either over or very near the internal cervical os.
There are four types of placenta previa depending upon the degree of extension of the placenta to the lower segment.

Type—I (Low-lying): The major part of the placenta is attached to the upper segment and only the lower margin encroaches onto the lower segment but not up to the os.
Type—II (Marginal): The placenta reaches the margin of the internal os but does not cover it.
Type—III (Incomplete or partial central): The placenta covers the internal os partially (covers the internal os when closed but does not entirely do so when fully dilated).
Type—IV (Central or total): The placenta completely covers the internal os even after it is fully dilated.

Oppenheimer classification of placenta previa

The distance of the placenta  from OS Pregnancy outcome
> 20 mm from Os Cesarean section not indicated
11-20 mm from Os Low risk of cesarean section  and bleeding
0-10 mm from Os High risk of cesarean section and bleeding
Overlapping os by any distance Caesarean indicated


Degree of placenta previa Type
Mild Type I, Type II Anterior
Major Type II posterior, Type III, Type IV

At mid-pregnancy, around 12 percent of pregnant ladies have placenta previa. Placentas that lie close to but not over the internal os up to the early third trimester are unlikely to persist as a Previa by term.
The second-trimester low-lying placenta is associated with antepartum admission for hemorrhage and increased blood loss at delivery.

A dangerous type of placenta previa
Curved birth canal major thickness of the placenta (about 2.5 cm) overlies the sacral promontory, thereby diminishing the anteroposterior diameter of the inlet and prevents engagement of the presenting part. This hinders effective compression of the separated placental site to stop bleeding.

The placenta is more likely to be compressed if vaginal delivery is allowed. More chance of cord compression or cord prolapses may produce fetal anoxia or even death.
Risk factors for placenta previa:
Older age
Multiple gestations
Previous cesarean delivery
Previous uterine curettage.
Chronic hypertension
Cigarette smoking
Drug abuse(especially cocaine)
History of abortion
Previous placenta previa and
Assisted conception

Clinical features
Bleeding is the main symptom in placenta previa which is painless, apparently causeless, and recurrent. Approximately two-thirds of the patient with placenta previa bleed. A pregnant lady usually does not bleed until near the end of the second trimester or later. Bleeding occurs in placenta previa because when the internal os dilates, and some of the implanted placentae inevitably separate.

Bleeding that ensues is augmented by the inherent inability of myometrial fibers in the lower uterine segment to contract and thereby constrict avulsed vessels. Similarly, bleeding from the lower segment implantation site also frequently continues after placental delivery.

Warning hemorrhage is the bleeding in about 5% cases, especially in primigravidae which occurs for the first time in the cases in placenta previa which is usually slight. In about one-third of cases, there is a history of “warning hemorrhage”.

The term Sentinel bleed is the bleeding from a lady with placenta Previa usually begining without warning and without pain or contractions in a woman who has had an uneventful prenatal course and is rarely so profuse as to prove fatal. Usually, it ceases, only to recur. In perhaps 10 percent of women, particularly those with a placenta implanted near but not over the cervical os, there is no bleeding until labor onset.

Abdominal examination:
On abdominal examination of the abdomen of a pregnant lady with placenta previa height of the uterus is proportionate to gestational age. Feel of the uterus is soft and relaxed. Sometimes fetal malpresentation may be noted (in 1/3rd of the case). The fetal head is found to be high floating.

Routine placental localization is considered part of the anomaly scan at 20 to 22 weeks’ gestation in many centers. Unfortunately, the earlier the scan is performed, the more likely the placenta is to be found in the lower pole of the uterus. For example, approximately 28% of placentas in women who undergo transabdominal scanning before 24 weeks are “low,” but by 24 weeks, this number drops to 18%, and only 3% are low-lying by term.

A definitive diagnosis is made by an internal examination that is a double set up examination which is done in the operation theatre, where one can feel the placental tissue instead of the fetal presenting part. We can also diagnose placenta previa by direct visualization during the cesarean section and examination of the placenta following vaginal delivery.
1. Expectant management is done provided the following conditions:

  • The duration of pregnancy is less than 37 weeks.
  • Active vaginal bleeding is absent.
  • Assure fetal well-being  (USG).
  • For stable women i ,e hemoglobin > 10 g%; hematocrit > 30%

a) Inpatient management:
Macafee and Johnson’s regime is followed for pregnancies remote from the term in an attempt to improve the fetal salvage without increasing undue maternal hazards. The aim is to continue the pregnancy for fetal maturity without compromising maternal health.

We need to hospitalize the pregnant lady, include easy access to resuscitation, ensure bed rest, limitation of activities, and transfuse blood to maintain hemoglobin of at least 10 g/dL or hematocrit of 30%.

b) Outpatient management is for stable women with home support,  proximity to the hospital, and easy access to transportation and telephone.

2. Definitive management
Cesarean section is needed if :

  • Bleeding occurs at or after 37 weeks of pregnancy
  • The patient is in labor if the patient is in the exsanguinated state on admission
  • Bleeding is continuing and of moderate degree
  • and the fetus is dead or known to be congenitally deformed.

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