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
Presentation of placenta praevia?
- Most asymptomatic
- Painless vaginal bleeding (antepartum haemorrhage): usually later in pregnancy (around or after 36 weeks)
How is placenta praevia often identified?
Placenta praevia is often identified before symptoms develop during a routine ultrasound appointment: anomaly scan.
When symptoms do present in placenta praevia, when do they typically occur?
3rd trimester
What is the main clinical feature of placenta parevia?
Painless vaginal bleeding: can range from spotting to life-threatening haemorrhage
Examination findings in placenta praevia?
- no evidence of a vaginal or cervical cause of the bleeding
- the uterus is not typically painful, unless in labour
What should be avoided in placenta praevia?
1) vaginal & rectal exams
2) intercourse
What investigation is used to diagnose placenta praevia?
Ultrasonography:
1) Transabdominal ultrasound detects placenta praevia in approximately 95% of cases
2) Transvaginal ultrasound detects the condition in almost 100% of patients.
What date is the routine anomaly scan?
Around 20 weeks
If placenta praevia/low lying uterus is found at anomaly scan, what is next step?
1) Follow-up transvaginal ultrasound at 32 weeks: to identify if case has resolved or not
2) If persisent: follow up subsequent transvaginal ultrasound to plan delivery at 36 weeks
If persistent placenta praevia is then identified at follw up transvaginal ultrasound at 32 weeks, what is next step?
Follow up at 36 weeks for a subsequent transvaginal ultrasound to plan delivery.
Depending on severity of bleeding in placenta praevia, what further investigations can be done?
1) FBC: maternal anaemia or platelet disorder
2) Clotting studdies: may aid in identifying bleeding disorders, but are only indicated if the platelet count is abnormal
3) Blood type and cross-match: required in preparation for surgery
4) The Kleihauer test: used in rhesus-negative mothers to determine the dose of anti-D required
5) Fetal cardiotocography (CTG): recommended for patients admitted to hospital to assess fetal wellbeing and aid in decision making
6) Biochemistry such as liver function tests and urea & electrolyte levels: can help rule out hypertensive disorders such as pre-eclampsia
Define antepartum haemorrhage
Bleeding after 28 weeks gestation
Give some differentials for placenta praevia
Other causes of antepartum haemorrhage and other placenta abnormalities:
1) Placental abruption
2) Miscarriage
3) Placenta accreta
4) Local causes of antepartum haemorrhage e.g. genital lesions (benign and malignant), genital lacerations and trauma, cervical ectropion and local infections.
Differentiating factors between placenta praevia and placental abruption:
a) pain
b) volume of bleeding
c) uterus on exam
d) US assessment
a)
placenta praevia: painless
placental abruption: painful
b) in both cases, volume of bleeding is incredibly variable
c) placental abruption: uterus more likely to be tense on examination
d) placental abruption: will show separation of the placenta from the uterine wall
Can placenta praevia and abruption co-exist in the same patient?
Yes
What is placental abruption?
Occurs when the placenta detaches from the endometrium and results in haemorrhage at the site of detachment.
Differentiating factors between placenta praevia and miscarriage:
a) bleeding
b) pain
c) when?
a)
miscarriage: sometimes accompanied by expulsion of products of conception
b)
placenta praevia: painless
miscarriage: often occurs alongside cramp-like abdominal pain
c)
placenta praevia: 3rd trimester
miscarriage: more common in 1st and 2nd trimesters
What examination signs of miscarriage may be present?
1) Cervical os may be open
2) Identification of products of conception
3) Uterine changes
Management of placenta praevia?
1) ABCDE if serious haemorrhage
2) Planned delivery with C section
3) Emergency caesarean section may be required with premature labour or antenatal bleeding.
4) Corticosteroids: where the gestational age is below 34 weeks
5) Tocolytics
6) Anti-D should be given with 72 hours of onset of bleeding in any resus negative mother
When should corticosteroids be given in placenta praevia?
Why?
Corticosteroids are given between 34 and 35 + 6 weeks gestation to mature the fetal lungs, given the risk of preterm delivery.
When is planned delivery considered in placenta praevia?
Planned delivery is considered between 36 and 37 weeks gestation.
It is planned early to reduce the risk of spontaneous labour and bleeding.
Purpose of given tocolytics in placenta praevia?
Tocolytics may be used to delay labour to provide maximum benefit from corticosteroids therapy
When should anti-D be given in any resus negative mother?
Anti-D should be given with 72 hours of onset of bleeding
Delivery in patients with minor placenta praevia (e.g. low lying placenta)?
Close monitoring - can deliver normally, however there is an increase risk of a requiring cesarean delivery.
What is the main complication of placenta praevia?
Haemorrhage: before, during and after delivery.
Management options of haemorrhage in placenta praevia?
1) Emergency caesarean section
2) Blood transfusions
3) Intrauterine balloon tamponade
4) Uterine artery occlusion
5) Emergency hysterectomy
Complications of placenta praevia?
1) Haemorrhage: risk increased by low pre-bleed maternal haemoglobin and iron stores.
2) Pre-term birth
3) Risks of c section
4) Foetal death
5) Intrauterine growth restriction
What is placenta abruption?
Refers to when the placenta separates from the wall of the uterus during pregnancy.
The site of attachment can bleed extensively after the placenta separates.
Placental abruption is a significant cause of antepartum haemorrhage.
What happens in placental abruption?
There is a compromise of the vascular structures supporting the placenta, which results in premature separation of the placenta from the normal lining of the uterus.
Onset of placenta praevia?
Often acute
Risk factors for placental abruption?
1) Chorioamnionitis: an infection of the placenta and the amniotic fluid
2) Alcohol ingestion
3) Pre-eclampsia
4) Overt HTN
5) Smoking
6) Advanced maternal age: happens more frequently in women >/= 35 BUT usually this has been attributed to multiparity (three or more deliveries) independent of age.
7) Cocaine use during pregnancy
8) Abdominal trauma: consider domestic violence
9) Previous placental abruption
How can chorioamnionitis lead to abruption of the placenta?
Bacterial colonisation at decidua may initiate inflammation of placental tissues and finally leads to the abruption of the placenta.