Keep close eye on placenta praevia

BASICS

Placenta praevia must be closely observed during pregnancy, advises Dr Aruna Sharma.

Placenta praevia is defined as the implantation of the placenta over or near the internal os of the cervix. The placenta can completely cover the os (total placenta praevia); the placental edge can partially cover the os (partial placenta praevia); or it can approach the border of the os (marginal placenta praevia).

Placenta praevia is a significant cause of maternal and perinatal mortality and morbidity.

Possible causes include a scarred endometrium, a large placenta, an abnormal uterus, or abnormal formation of the placenta. Its incidence is approximately one out of 200 births. In primigravidas, the incidence is as low as 0.2 per cent.

Clinical features

The incidence increases with each pregnancy, and it is estimated that women who have had six or more previous deliveries may be at risk in as many as one in 20 births. The incidence of placenta praevia doubles in multiple pregnancies.

Risk factors for the condition include previous placenta praevia, first subsequent pregnancy following a caesarean delivery, advanced maternal age, multiple pregnancies, previous induced abortion and smoking.

The manifestations of placenta include spotting during the first and second trimester, sudden, painless, and profuse vaginal bleeding in the third trimester (usually after 28 weeks), and uterine cramping occurring with onset of bleeding. The uterus is usually soft and relaxed. In 15 per cent of cases the infant position is oblique or transverse.

The time of first bleed in cases of placenta praevia (28 to 30 weeks) correlates with the stage of gestation during which the lower uterine segment begins to elongate, accounting for some degree of separation.

However, up to 10 per cent of placenta praevia pregnancies may go to 38 weeks gestation without clinical bleeding.

Management

It is safe to perform a transvaginal ultrasound is safe in the presence of placenta praevia, because it is more accurate than transabdominal ultrasound in locating the placenta.

Although about 5 per cent of women have ultrasound evidence of a low placenta at 16-18 weeks' gestation, only 10 per cent of these will actually have a placenta praevia at delivery.

Management depends on the stage of pregnancy and the extent of haemorrhage.

It is preferred to allow the pregnancy to continue up to a point at which the baby is less likely to encounter major complications of pre-immaturity after birth.

Management of placenta praevia is expectant and involves avoidance of digital examination. Any significant bleed in placenta praevia is managed by blood transfusion and close observation in hospital.

Mode of delivery should be based on clinical judgment in each case, but a placenta praevia encroaching within 2cm of internal os is a contraindication to vaginal delivery.

Women who have previously had a caesarean section and who have placenta praevia subsequently should be considered to be at high risk of having placenta accrete, increta and percreta (a morbidly adherent placenta), which should be confirmed by ultrasound imaging. Senior anaesthetic and obstetric input are vital in planning the delivery.

Antenatal counselling

Before the delivery, all women with placenta praevia and their partners, should have had counselling about the mode of delivery and possible blood transfusion requirement.

In the community, the GP taking care of these women should be vigilant in identifying anaemia early and act accordingly.

- Dr Sharma is a specialist registrar in obstetrics and gynaecology at City Hospital, Birmingham

KEY POINTS

- Diagnosis should be made through transvaginal ultrasound, which is safe and accurate.

- During a placenta praevia pregnancy the fist significant bleeding episode usually takes place at 28-30 weeks' gestation.

- Before delivery, the women and their partners should have counselling on possible blood transfusion requirements.

- The GP taking care of these women should be vigilant in identifying anaemia early.

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