Antenatal Care: Placenta Praevia & Plancetal Abruption Flashcards
What is placenta praevia?
Where the placenta is attached in the lower portion of the uterus, overlying the cervical os (lower than the presenting part of the fetus).
What is the most common a type of abnormal placental location?
Placenta praevia
Placenta praevia affects what % of pregnances?
0.5% - however incidence is rising.
What % of placenta praevia will resolve spontaneously?
Up to 90% of cases resolving spontaneously before becoming symptomatic - as the uterus grows and the placenta migrates upwards relative to the cervical os.
Risk of placenta praevia?
The condition is a major cause of maternal and fetal mortality and morbidity: cause of antepartum haemorrhage, vaginal bleeding in the 3rd trimester and indication for caesarean section
Definition of low lying placenta vs placenta praevia?
Low lying placenta: when the placenta is within 20mm of the internal cervical os
Placenta praevia: used only when the placenta is over the internal cervical os
What are the 3 causes of antepartum haemorrhage?
1) Placenta praevia
2) Placenta abruption
3) Vasa praevia
What are some causes of spotting or minor bleeding in pregnancy?
1) Cervical ectropion
2) Infection
3) Vaginal abrasions from intercourse or procedures.
Risks of placenta praevia?
1) Antepartum haemorrhage
2) Emergency C section
3) Emergency hysterectomy
4) Maternal anaemia and transfusions
5) Preterm birth and low birth weight
6) Stillbirth
What is the most important risk factor for placenta praevia?
Previous uterine scarring: typically the result of a C section (but other causes possible).
Risk factors for placenta praevia?
1) previous uterine scarring e.g. previous caesarean sections, previous placenta praevia
2) older maternal age
3) multiple pregnancies
4) large number of previous pregnancies
5) smoking
6) assisted reproduction (e.g. IVF)
7) structural uterine abnormalities (e.g. fibroids)
At what scan is the position of the placenta assessed in pregnancy?
20 week anomaly scan: assess the position of the placenta and diagnose placenta praevia.
Pathophysiology of placenta praevia?
1) Occurs when the blastocyst, which later develops into the placenta, implants into the lower uterine segment.
2) This can result in the placenta overlying the cervical os and obstructing the pathway of the fetus during labour.
Cause of bleeding in placenta praevia?
Number of reasons:
1) As the placenta is in a vulnerable location, bleeding can be triggered by pressure around the cervix causing minor placental trauma e.g. penetrative sex, vaginal exam
2) Labour & delivery:
- The placenta is at risk of rupture because it is blocking the path of the fetus
- This may results in massive haemorrhage from both the mother and fetus, leading to death
What is the classification of placenta praevia based on?
Based the relationship and distance between the placenta and the cervical os.
What are the 4 grades of placenta praevia?
Grade I: low lying placenta
Grade II: marginal praevia
Grade III: partial praevia
Grade IV: complete praevia
Describe grade I of placenta praevia
Low lying placenta:
a) The placenta is in the lower uterine segment but NOT reaching the internal cervical os
b) The lower edge of the placenta is 0.5-2cm from the internal cervical os
How far is the lower edge of the placenta from the internal cervical os in Grade I placenta praevia?
0.5 - 2cm
Describe grade II of placenta praevia
Marginal praevia:
a) The lower edge of the placenta reaches the internal cervical os
b) The placenta extents to the margin of the os but does not cover it
describe grade III of placenta praevia
Partial praevia: the placenta is partially covering the internal cervical os
Describe grade IV of placenta praevia
Complete praevia: the placenta completely covers the internal cervical os
How does the grade of placenta praevia affect prognosis?
Prognosis worsens with higher grades.
- Low lying placentas are found in 4-6% of pregnancies before 20 weeks, however up to 90% of these spontaneously resolve
- However, only 10% of complete praevias resolve.
What do all unresolved cases of complete praevia require?
Cesarean delivery
The RCOG guidelines (2018) recommend against using this grading system for placenta praevia now.
What 2 descriptions are more commonly used?
1) low-lying placenta
2) placenta praevia