From Wikipedia, the free encyclopedia
Placenta praevia (
placenta previa AE) is an
obstetric complication in which the
placenta is attached to the
uterine wall close to or covering the
cervix.
[1]
It can sometimes occur in the later part of the first trimester, but
usually during the second or third. It is a leading cause of
antepartum haemorrhage (
vaginal bleeding). It affects approximately 0.5% of all
labours.
Placenta praevia is hypothesized[
who?] to be related to abnormal
vascularisation of the
endometrium caused by scarring or
atrophy from previous trauma, surgery, or infection.
In the last trimester of pregnancy the
isthmus of the
uterus
unfolds and forms the lower segment. In a normal pregnancy the placenta
does not overlie it, so there is no bleeding. If the placenta does
overlie the lower segment, as is the case with placenta praevia, it may
shear off and a small section may bleed.
Diagnosis
Women with placenta praevia often present with painless, bright red
vaginal bleeding. This bleeding often starts mildly and may increase as
the area of placental separation increases. Praevia should be suspected
if there is bleeding after 24 weeks of gestation. Abdominal examination
usually finds the uterus non-tender and relaxed. Leopold's Maneuvers
may find the fetus in an oblique or breech position or lying transverse
as a result of the abnormal position of the placenta. Praevia can be
confirmed with an ultrasound.[2]
In parts of the world where ultrasound is unavailable, it is not
uncommon to confirm the diagnosis with an examination in the surgical
theatre.
The proper timing of an examination in theatre is important. If the
woman is not bleeding severely she can be managed non-operatively until
the 36th week. By this time the baby's chance of survival is as good as
at full term.
Placenta previa is classified according to the placement of the placenta:
- Type I or low lying: The placenta encroaches the lower segment of the uterus but does not infringe on the cervical os.
- Type II or marginal: The placenta touches, but does not cover, the top of the cervix.
- Type III or partial: The placenta partially covers the top of the cervix
- Type IV or complete: The placenta completely covers the top of the cervix
Placenta previa occurs approximately one of every 250 births. One third of all antepartum hemorrhage occurs due to placenta previa.[citation needed]