Abnormalities in placentation

Question 1

Definition of placenta praevia

Answer 1

Using TVUSS as a placenta developing within the lower uterine segment and covering or encroaching on the cervical os. For pregnancies greater than 16 weeks of gestation, the placenta should be reported as ‘low lying’ when the placental edge is less than 20mm from the internal os, and normal when the placental edge is 20mm or more from the internal os on TVUSS or abdominal USS.

Question 2

Definition of resolved praevia

Answer 2

low-lying placenta seen in early pregnancy that has migrated away from the cervical os

Question 3

Incidence of placenta praevia

Answer 3

1 in 200 pregnancies

Question 4

Risk factors for placenta praevia

Answer 4

Caesarean section (increased risk in subsequent pregnancies), Anti-retroviral therapy (ART), Advanced maternal age, increasing parity, maternal smoking, structural uterine abnormalities (fibroids), IVF

Question 5

How can placenta praevia be graded

Answer 5

According to abdominal USS- grades 1-2 referred to as ‘minor’ and 3-4 referred to as ‘major’
* Grade I or minor praevia- lower edge inside the lower uterine segment
* Grade II or marginal praevia- lower edge reaching the internal os
* Grade III or partial praevia- placenta partially covers the cervix
* Grade IV or complete praevia when placenta completely covers cervix

Question 6

Pathophysiology of placenta praevia

Answer 6

• Occurs when the blastocyst implants into the lower uterine segment near the cervical os- most cases are probably accidental and simply result from normal variation in placentation
• In PP, the placenta is partly or completely covering the os and is in front of the presenting part of the foetus
• Bleeding may occur spontaneously, from placental trauma (intercourse, vaginal examination) or as the cervix opens at the onset of labour
• As the presenting part moves into the lower uterine segment, the placenta may be torn or may separate (abrupt) from the uterus
• Massive haemorrhage results from both the mother and the foetus

Question 7

Complications of placenta praevia

Answer 7

• Associated with increased morbidity and mortality for mother and foetus
• Antepartum haemorrhage
• Emergency C-section and hysterectomy
• Maternal aneamia and transfusions
• Preterm birth, LBW and stillbirth

Question 8

Presentation of placenta praaevia

Answer 8

• May be identified at the mid-pregnancy routine foetal anomaly scan (which includes placental localisation)
• If the placenta is thought to be low lying (less than 20 mm from the internal os) or praevia (covering the os) at the routine fetal anomaly scan, a follow-up ultrasound examination including a TVS is recommended at 32 weeks of gestation to diagnose persistent low-lying placenta and/or placenta praevia
• Many women are asymptomatic. It may present with painless vaginal bleeding (antepartum haemorrhage)- bleeding usually occurs later around or after 36 weeks
• Bleeding may be recurrent and be provoked by sex or onset of labour
• In 35% of cases, foetus is malpositioned

Question 9

Investigations for placenta praevia

Answer 9

• TVUSS for the diagnosis of placenta praevia or a low-lying placenta is superior to transabdominal and transperineal approaches and is safe
• In women with a persistent low-lying placenta or placenta praevia at 32 weeks who remain asymptomatic, require an additional TVUSS at 36 weeks to inform discussion about mode of delivery
• A short cervical length on TVUSS before 34 weeks increases the risk of preterm emergency delivery and massive haemorrhage at caesarean section
• FBC and group and save
• AVOID VAGINAL AND RECTAL EXAMINATION and advise patient to avoid penetrative sex

Question 10

How should asymptomatic placenta praviea identified at 20 week scan be managed

Answer 10

• Rescan at 32 weeks and again at 36 weeks if still low-lying
• Delivery should then be considered between 36+0 and 37+0 weeks of gestation
• The mode of delivery should be based on the clinical background, the women’s preferences and USS findings including distance between placental edge and fetal head (elective c-section)

Question 11

How is method of delivery affected by placeta praevia

Answer 11

• All women and their partners should have a discussion about indications for blood transfusions and hysterectomy
• Regional anaesthesia is considered safe and is associated with lower risks of haemorrhage than general anaesthesia for caesarean delivery in women with placenta praevia or a low-lying placenta (may require switch to GA)
• Should consider using preoperative and/or intraoperative USS to determine placental location and find the optimal place for uterine incision (should consider vertical incisions when the foetus is in a transverse lie)
• If pharmacological measures fail to control haemorrhage, initiate intrauterine tamponade and/or surgical haemostatic techniques sooner rather than later
• Should consider hysterectomy early
• Delivery should be arranged in a maternity unit with on-site blood transfusion services and access to critical care
• May attempt vaginal birth if the foetal head is below the leading edge of the placenta as the foetal head can access the birth canal without placental seperation

Question 12

How should symptomatic women be managed

Answer 12

• ABCDE assessment and continuous foetal monitoring
• If the mother is haemodynamically unstable or there is evidence of foetal distress-> expedite delivery (irrespective of gestation)
• Late preterm (34+0 to 36+6 weeks) delivery should be considered for women presenting with a history of vaginal bleeding or other associated risk factors for preterm delivery
• A single course of antenatal corticosteroid therapy is recommended between 34+0 and 35+6 weeks of gestation for pregnant women with a low-lying placenta or placenta praevia and is appropriate prior to 34+0 weeks of gestation in women at higher risk of preterm birth (in this case can give tocolysis for 48 hours to administer corticosteroids)

Question 13

How should women with asymptomatic placenta praevia be safetynetted

Answer 13

All woman being treated at home in the third trimester should attend the hospital immediately if she experiences any bleeding, including spotting, contractions or pain

Avoid having sex

Advise that 90% of placentas will move away from the Os

Question 14

Definition of vasa praevia

Answer 14

Occurs when the foetal vessels run through the free placental membranes.
Since it is unprotected by placental tissue or Wharton’s jelly (soft protective layer) of the umbilical cord, a vasa praevia is likely to rupture in active labour or after an amniotomy for augmentation for labour (particularly when located near or over the cervix.)

Question 15

What do the foetal vessels consist of

Answer 15

The two umbilical arteries and the single umbilical vein

Question 16

What might cause vasa praevia

Answer 16

May be due tovelamentous insertion of the umbilical cord (umbilical cord inserts into foetal membranes then travels within the membrane to the placenta) OR where vessels join an accessory (succenturiate) placental lobe

Question 17

Risk factors for vasa praevia

Answer 17

Low lying placenta (present in around 60% of cases), IVF or assisted pregnancy, multiple pregnancy

Question 18

Incidence of vasa praevia. What is the prognosis

Answer 18

Between 1 in 1200 and 1 in 5000 pregnancies. The fetal mortality rate in this situation is at least 60% despite urgent caesarean delivery. However, improved survival rates of over 95% have been reported where the diagnosis has been made antenatally by ultrasound (often not possible)

Question 19

Presentation of vasa praevia

Answer 19

• Can be diagnosed during early labour by vaginal examination, detecting the pulsating foetal vessels inside the internal os
• May also present with dark-red vaginal bleeding and acute foetal compromise after spontaneous or artificial rupture of membranes

Question 20

Classification of vasa praevia

Answer 20

Type I vasa praevia – the fetal vessels are exposed as a velamentous umbilical cord
Type II vasa praevia – the fetal vessels are exposed as they travel to an accessory placental lobe

Question 21

Investigations for vasa praevia when undiagnosed at pregnancy

Answer 21

• Placental pathological examination should be performed to confirm the diagnosis of vasa praevia, in particular when stillbirth has occurred or where there has been acute fetal compromise
• Because of the speed at which foetal exsanguination (severe loss of blood) can occur and the high perinatal mortality rate associated with ruptured vasa praevia, delivery should not be delayed whilst trying to confirm the diagnosis if there is evidence of foetal distress

Question 22

Management of vasa praevia

Answer 22

• In confirmed vasa praevia- elective C-section should be carried out before the onset of labour
• In asymptomatic women- planned C-section is reasonable between 34-36 weeks gestation
• Can consider prophylactic hospitalisation from 30-32 weeks of gestation (threshold lowered by antenatal bleeding, threatened premature labour, multiple pregnancy)
• Emergency C-section should be performed after: SROM, labour at a viable age
• Administration of corticosteroids for foetal lung maturity is recommended from 32 weeks gestation due to risk of prematurity
• Should confirm persistence of vasa praevia by USS in the third trimester

Question 23

Definition of placenta accreta

Answer 23

A spectrum disorder ranging from abnormally adherent to deeply invasive placental tissue.

Question 24

What are the divisions of placenta accreta spectrum

Answer 24

• Superficial placenta accreta: chorionic villi attach to the myometrium, rather than being restricted to the decidua basalis (more adherent)
• Placenta increta: Chorionic villi invade into the myometrium
• Placenta percreta: Chorionic villi invade through the perimetrium

Question 25

Risk factors for placenta accreta

Answer 25

History of accreta spectrum in a previous pregnancy, placenta praevia, increased maternal age, previous caesarean delivery and other uterine surgery (including endometrial curettage). Risk increases with the number of previous C-sections

Question 26

When should women be informed of the risk of placenta ccreta

Answer 26

Women requesting elective c-section for non-medical indications

Question 27

Pathophysiology of placenta accreta

Answer 27

• During the 3rd stage of labour, normal placental separation occurs along a physiological plane of cleavage which is formed by vascular networks between the basal plate and uterine wall.
• In placenta accreta spectrum the physiological plane of cleavage is deficient and results in failure of placental separation after birth
• Partial/total absence of the decidua basalis and ‘Nitabuch’s layer’ allows the chorionic villi to invade into the myometrium
• Improper separation of the placenta during labour leads to significant risk of PPH

Question 28

Investigation for placenta accreta

Answer 28

• Antenatal diagnosis of placenta accreta spectrum is crucial in planning management and has been shown to reduce morbidity and mortality
• Previous caesarean delivery and presence of anterior low-lying or placenta praevia are warning signs for accreta spectrum

Diagnosis can be made with USS, MRI and Doppler studies
* MRI can be used to complement USS to assess the depth of invasion and lateral extension of myometrial invasion (especially with posterior placentation)
* USS signs include: loss of ‘clear zone,’ abnormal lacunae, myometrial thickening, placental bulge, focal exophytic mass (breaking into the uterine serosa and extending beyond it)

Question 29

Management of placenta accreta

Answer 29

• Women diagnosed with accreta spectrum should be cared for by an MDT team in a specialist centre (delivery should take place at a specialist centre with expertise on its management- should have access to ITU and NICU)
• In the absence of risk factors for preterm birth, planned delivery at 35+0 to 36+6 is appropriate
• Should have a contingency of emergency c-section (should be counselled on risk of lower urinary tract damage, need for blood transfusion and hysterectomy etc.)

Surgical approach:
* Caesarean section hysterectomy with the placenta left in situ is preferable to attempting to separate it from the uterine wall
* When the extent of the accreta is limited in depth and surface area, the entire placentation area can be visualised and is accessible, uterus preserving surgery may be possible (partial myometrial resection)
* Uterus preserving surgery should NOT be attempted in placenta percreta
* If the placenta is left in situ, local arrangements need to be made for regular review, access to emergency care etc (can be attempted if woman wishes to preserve fertility, BUT high risk of bleeding etc.)
* If placenta accreta is found when opening the abdomen for an elective c section, the abdomen should be closed, and delivery delayed
* If placenta accreta is discovered after delivery of the baby, a hysterectomy is recommended.