placenta previa

Placenta Previa

Definition

Attachment of the placenta to the lower segmet of the uterus

Incidence

0.5% of pregnancies

More common in multipara

More common in twin pregnancies due to the large size of the placenta

Aetiology

Low implantation of the blastocyst

Development of the chorionic villi in the decidua capsularis to leading to attachment to the lower uterine segment

Large placenta as in twin pregnancy

Types

First Degree (Type I / PP lateralis / low lying placenta)

The lower edge of the placenta reaches the lower uterine segment but not the internal os

Second Degree (Type II /PP marginalis)

The lower edge of the placenta reaches the margin of the internal os but does not cover it

Third Degree (Type III / PP incomplete Centralis)

Placenta covers part of the cervical os; the placenta covers the internal os partially dilated but not when it is fully dilated

Fourth Degree (Type IV / PP Complete centralis)

Placenta completely covers the os, even when the cervix is dilated; the placenta covers the internal os completely whether the cervix is partially or fully dilated

Placenta previa marginalis posterior has worse prognosis than marginalis anteriror since it encroaches on the true conugate diameter delaying engagement of the head and engangement of the head will compress the placenta against the sacrum, causing fetal asphxia

Mechanism of Bleeding

During the third trimester and labour there is progressive stretching of the lower uterine. The segment placenta is non elastic and cannot stretch with the lower segment. So there is separation of a part of the placenta with bleeding. As the labour progresses there is there is more separation of the placenta and more bleeding.

Symptoms and Signs

Causeless, Painless and Recurrent bright red vaginal bleeding.

Bleeding may follow sexual intercourse.

It is painless but labour pains will be there.

Fortunately the first bleeding is usually not severe

Shock may follow if the bleeding is severe

Anemia if the blood loss is recurrent

The uterus size is corresponding to the gestational age, relaxed and non-tender

Fetal parts and FHS are easily detected

Malpresentation like transvers lie or oblique lie or breech presentation may be present

The head may not engage due to placenta occupying the lower segment

Any PV examination may provoke severe bleeding; can be done only in OT under GA with cross matched blood in hand and when everything is ready for a Caesarian Section : when the index finge is inserted gently the placenta can be felt as a tough fibrous mass

Investigations

USGM : The lower edge of the placenta is less than 3 cm from the margin of the internal os

The posterior placenta is obscured by the fetus: use head down tilt of the mother or displace the fetus manually to visualize. The distance of the presenting part from the sacral promontory is > 1.5 cm

With increasing gestational age and the formation of the lower uterine segment, a gap develops between the placental edge and the internal os "placental migration". So it is recommended to repeat scan when placenta is diagnosed in mid-pregnancy

Management

Admit when bleeding occurs

No PV

No vaginal pack

Sterile vulval pad permitted

No oral intake allowed as anesthesia may be required

Be ready to combat shock

Get at least two units of blood ready

USGM to differentiate between abruptio placentae and placenta previa

Assess fetal viability age, position and presentation.

Assess the amount of bleeding

Be ready for an emergency CS

If 37 weeks induction or CS

Conservative Treatment

Hopitaliz, bed rest, monitor fetal well being, care of anemia, Anti-D immunoglobulin if Rh-negative mother

If in labour PV with precautions mentioned above

Decide whether to induce labor by amniotomy + oxytocin or CS

Vaginal delivery is allowed if

Plcenta is lateralis or marginalis anterior
Bleeding is very little
Vertex presentation
Adequate pelvis witn no soft tissue obstruction
Partially dilated cervix to allow amniotomy

Caesarean section is indicated in

Placenta previa centralis whether complete or incomplete even if the fetus is dead.

Placenta previa marginalis posterior

Severe bleeding

Presentation is other than vertex

Other obstetric indications lie contracted pelvis, cord prolapse or elderly primigravida

Vasa previa

Although upper segment C.Sl is sometimes advocated lower segment C.S. is prferable because it allows better control of bleeding from the placental site and it leaves a stronger scar; if placenta is anterior it is gently displaced laterally to reach the fetal head or it can be cut through; the latter is not preferred.

Complications of Placenta Previa

Maternal mortality is 0.2%

During pregnancy