Placenta praevia (placenta previa AE) is a obstetric complication that can occur in the second or third trimester of pregnancy. It is a leading cause of antepartum haemorrhage (vaginal bleeding) and is characterised by the implantation of the placenta over or near the top of the cervix. It affects approximately 0.5% of all labours.
Pathophysiology
No specific cause of placenta praevia has yet been found but it is hypothesized to be related to abnormal vascularisation of the endometrium caused by scarring or atrophy from previous trauma, surgery, or infection.
Women with placenta praevia often present with bright red vaginal bleeding. 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 manoeuvres may find the fetus in a in an oblique or breech position or lying transverse because the abnormal position of the placenta. Praevia can be confirmed with an ultrasound.
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.
Risk Factors
The following have been identified as risk factors for placenta previa:
- Previous placenta praevia, caesarean delivery, or abortion.
- Women who have has previous pregnancies, especially a large number of closely spaced pregnancies, are at higher risk.
- Women who are younger than 20 are at higher risk and women older than 30 are at increasing risk as they get older.
- Women with a large placentae from twins or erythroblastosis are at higher risk.
- Women who smoke or use cocaine may be at higher risk.
- Race is a controversial risk factor, with some studies finding minorities at higher risk and others finding no difference.
Intervention
An initial assessment to determine the status of the mother and fetus is required. Although mothers used to be treated in hospital from the first bleeding episode until birth, it is now considered safe to treat on an out patient basis if the fetus is at less than 37 weeks of gestation and neither the mother or the fetus are in distress.
Immediate delivery of the fetus may be indicated if the fetus is mature or if the fetus or mother are in distress. Blood volume replacement and to maintain blood pressure and blood plasma replacement to maintain fibrinogen levels may be needed. Vaginal birth is usually preferred over caesarian unless there is fetal distress. Caesarian section is contraindicated in cases of disseminated intravascular coagulation.
Sources