Placenta Praevia

Placenta praevia exists when the placenta is inserted wholly or in part into the lower segment of the uterus. Symptomatic placenta praevia is associated with the sudden onset of painless bleeding in the
second or third trimester. Women with placenta praevia are reported to be 14 times more likely
to bleed in the antenatal period compared with women without placenta praevia.¹

• If the placenta lies over the cervical os, it is considered a major praevia, if not, then minor praevia.
• The diagnosis is determined by ultrasound imaging relating the leading edge of the placenta to the cervical os.²
• Placental migration occurs during the second and third trimesters, as a result of the development of the lower uterine segment, but it is less likely if the placenta is posterior or if there has been a previous caesarean section.²

• The overall incidence is 1/200 births, and 1/1000 are total with placenta over entire cervix.³

Risk factors¹

• Prior history of placenta praevia
• Advancing maternal age
• Increasing parity
• Smoking
• Cocaine use
• Previous caesarean section
• Prior spontaneous or induced abortion

• Incidental finding on ultrasound.
• Painless bleeding starting after 28th week (although spotting may occur earlier) is usually the main sign. Typically it is sudden and profuse but usually does not last for long and so only rarely life-threatening.
• May be some initial pain in approximately 10% cases with coincidental placental abruption.
• In 25% cases, spontaneous labour appears in next few days.
• In a small proportion of cases, less dramatic bleeding occurs or does not start until spontaneous rupture of membranes or onset of labour.
• Uterus is often normal on palpation but unable to push high presenting part into pelvic inlet.
• In 15% of cases fetus presents in an oblique or transverse lie.
• Usually no indication of fetal distress unless complications occur.

• Ultrasound:
  • Can confuse blood clot in lower uterine segment for placenta.
• Transvaginal ultrasound is safe in the presence of placenta praevia and is more accurate than transabdominal ultrasound in locating the placenta.¹
• Other investigations will depend on context but may include full blood count, group and cross match, fetal monitoring.

The following is a suggested policy for screening from the Royal College of Obstetricians and Gynaecologists guideline:²

• Perform a transvaginal ultrasound scan on all women in whom a low-lying placenta is suspected from their transabdominal anomaly scan (at approximately 20-24 weeks).
• A further transvaginal scan is required for all women whose placenta reaches or overlaps the cervical os at their anomaly scan as follows (most low-lying placentas detected at a 20-week anomaly scan will resolve by the time the baby is born; therefore only a woman whose placenta extends over the internal cervical os should be offered another transabdominal scan:¹)
  • Women who bleed should be managed individually according to their needs.
  • In cases of asymptomatic suspected minor praevia, follow-up imaging can be left until 36 weeks.
  • In cases with asymptomatic suspected major placenta praevia, a transvaginal ultrasound scan should be performed at 32 weeks, to clarify the diagnosis and allow planning for third-trimester management and delivery.

• Inpatient management is recommended for women with symptomatic placenta praevia.¹ Women with major placenta praevia who have previously bled should be admitted and managed as inpatients from 34 weeks of gestation.
• Those with major placenta praevia who remain asymptomatic and have not had any vaginal bleeding, require careful counselling before contemplating outpatient antenatal care. Any home-based care requires close proximity with the hospital, the constant presence of a companion and full informed consent from the woman.
• Women managed at home should be encouraged to ensure that they have safety precautions in place, e.g. someone available to help them should the need arise have ready access to the hospital.
• Any woman being managed at home should attend hospital immediately if she experiences any bleeding, any contractions or any pain (including vague suprapubic period-like aches).
• Prior to delivery, all women with placenta praevia and their partners should have had antenatal discussions regarding delivery, haemorrhage, possible blood transfusion and major surgical interventions, such as hysterectomy.²
• Cervical cerlage reduces bleeding and prolongs pregnancy.²
• A placental edge less than 2 cm from the internal os is likely to need delivery by caesarean
  section, especially if it is posterior or thick.²
• Where possible, elective caesarean section should be deferred to 38 weeks to minimise neonatal morbidity.²

Acute bleeding

• Patient is admitted to hospital and vaginal examination avoided as may start torrential bleeding.
• Blood loss assessed and cross-matched for possible transfusion.
• In severe bleeding, baby is delivered urgently whatever its gestational age.
• In less severe bleeding, where fetus is at gestational age less than 36 weeks, expectant therapy is appropriate with women remaining in hospital.
• In many cases, pregnancy can continue to 36 weeks after which time the benefits of additional maturity need to be weighed against the risk of major haemorrhage and the possibility that repeated small haemorrhages may cause intrauterine growth retardation.
• Labour can then be induced at an optimal time decided upon by tests of fetal lung maturity (including assessment of amniotic fluid, surfactants and ultrasound growth measurements).

• Potentially fatal hypovolaemic shock resulting from severe antepartum, intra- or post-partum bleeding. Also infection and embolism.
• Rarely, placenta praevia accreta (placenta accreta is an abnormally firm attachment of the placenta to the uterine wall and the risk is increased in women with placenta praevia.
• Fetal haemorrhage, prematurity, intrauterine asphyxia or birth injury.

• A higher rate of pregnancy complications, including abruption placenta, antepartum haemorrhage and intrauterine growth restriction has been reported in women with low-lying placentas identified in the second trimester.¹
• The perinatal mortality rate associated with placenta previa ranges from 2-3%.
• Maternal mortality is 0.03% in the United States.