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Placenta Praevia and Accreta (GTG 27A - Sep 2018), Risk of Emergent Bleed…
Placenta Praevia and Accreta
(GTG 27A - Sep 2018)
Epidemiology
Increasing incidence due to rising rates of Caesarean sections, increased maternal age and use of assisted reproductive techniques
Incidence of placenta praevia at term
: 1 in 200 pregnancies
Incidence of placenta praevia with 1 previous C/S
: 10/1000 (1%)
Incidence of placenta praevia with 3 or more previous C/S
: 28/1000 (2.8%)
Prevalence of placenta accreta: 1:300 to 1:2000 pregnancies
Incidence of placenta accreta with praevia and no previous C/S
: 3.3-4%
Incidence of placenta accreta with 3 or more previous C/S
: 50-67%
Women with placenta praevia and previous C/S:
Risk of accreta for 1, 2, 3, 4, and 5 or more C/S is
3%, 11%, 40%, 61%, and 67%
respectively
Incidence of placenta accreta overall
: 1.7/10,000 (0.017%)
Incidence of placenta accreta with previous C/S and praevia
: 577/10,000 (5.77%)
Placenta accreta often remains undiagnosed before delivery in
50% to 66%
of cases
Risk Factors
Placenta Praevia
Caesarean section: Increased risk in subsequent pregnancies; risk increases as number of Caesarean sections increases
Maternal smoking
Assisted reproductive techniques
2nd pregnancy within 1 year of Caesarean section
Placenta Accreta
Previous history of placenta accreta
Caesarean section and other uterine surgery (e.g.: MROP, postpartum endometritis, myomectomy, endometrial curettage); risk increases as number of Caesarean sections increases (7 times after 1 previous C/S)
Placenta praevia
Advanced maternal age (35 or more)
Assisted reproductive techniques (especially IVF)
Uterine pathology: Bicornuate uterus, adenomyosis, subucous fibroids, myotonic dystrophy
Caesarean scar ectopic pregnancies
Definitions
Placenta Praevia
Low-lying placenta (>16 weeks)
: Placenta edge
<20mm
from the internal os on TAS/TVS
Placenta praevia
: Placenta lies directly over the internal os
Normal placenta (>16 weeks)
: Placenta edge
20mm or more
from the internal os on TAS/TVS
Placental "migration"
: Apparent migration following the development of the lower uterine segment during the 3rd trimester results in resolution of the low-lying placenta in
90% of cases before term
. This is less likely in women with previous C/S.
Twin pregnancies
: Likelihood of persistence of placenta praevia is dependent on gestational age. Majority of cases resolve by
32 weeks
.
After 32 weeks, 50% will resolve
, with no further changes after 36 weeks.
Placenta Accreta
Definition
: Abnormal adherence of the afterbirth in whole or in parts to the underlying uterine wall in the partial or complete absence of decidua
Creta
: Villi adheres superficially to the myometrium without interposing decidua
Increta
: Villi penetrate deeply intothe uterine myometrium down to the serosa
Percreta
: Villous tissue perforates through the entire uterine wall and may invade surrounding pelvic organs. High incidence of urological complications (cystotomy, ureteric injury) and intensive care admission.
May be subdivided into
total, partial, or focal
according to the amount of placental tissue involved
Investigations
Placenta Praevia
Fetal anomaly scan
: Placental localisation should be included to identify women at risk of low-lying placenta
Ultrasound at 32 weeks
: If placenta is low-lying or praevia at the fetal anomaly scan, follow-up ultrasound including TVS should be performed to diagnose persistent low-lying placenta or praevia.
Ultrasound at 36 weeks
: In asymptomatic women with persistent low-lying placenta or praevia at 32 weeks, TVS at 36 weeks is recommended to inform discussion about mode of delivery.
Transvaginal ultrasound (TVS)
Superior to transabdominal and transperineal approaches
Improves accuracy of placental localisation when placenta is posterior, maternal obesity, or presence of large uterine fibroids
Reclassifies 26-60% of placentas diagnosed as low-lying in 2nd trimester
PPV 93.3%, NPV 97.6%, false-negative rate 2.33%
Sensitivty 87.5%, specificity 98.8%
Cervical length measurements
:
May help facilitate management decisions in asymptomatic women
Short cervical length (<25mm) on TVS before 34 weeks
increases risk of APH, preterm emergency C/S, and massive haemorrhage at C/S
Serial TVS from 26 weeks
indicates that when cervical length decreases rapidly to
35mm or less
, there is increased risk of preterm C/S due to massive haemorrhage
Placenta Accreta
Previous C/S and the presence of a low-lying placenta or praevia should raise suspicion of placenta accreta. Refer to a specialist unit with imaging expertise.
Ultrasound
Sensitivity 90.72%; Specificity 96.94%
Abnormality of uterus-bladder interface
: Best specificity 99.75% for prediction of placenta accreta
Abnormal vasculature on colour Doppler
: Best predictive accuracy. Sensitivity 90.74%, specificity 87.68%.
Increased vascularity of placental bed with large feeder vessels entering lacunae. Placental lacunae give the placenta a moth eaten appearance on greyscale imaging.
With standardised ultrasound signs, performance of ultrasound is even higher:
Sensitivity 97% and specificity 97%
MRI
Diagnostic value of MRI and ultrasound is similar
May be used to complement ultrasound to assess the depth of invasion and lateral extension of myometrial invasion, epsecially with posterior placentation and/or signs suggesting parametrial invasion
Main MRI features
Abnormal uterine bulging
Dark intraplacental bands on T2 weighted imaging
Heterogeneous signal intensity within the placenta
Disorganised vasculature of placenta and disruption of uteroplacental zone
Sensitivity 75-100%; Specificity 65-100%
Management
Placenta Praevia
Venous thromboembolism
: Balance risk of developing VTE against risk of bleeding
Antenatal corticosteroids
Single course recommended
between 34 and 35+6 weeks
Can give
prior to 34 weeks
in women at higher risk of preterm birth
Associated with reduction in perinatal death, respiratory distress syndrome, intraventricular haemorrhage, and necrotising enterocolitis
Tocolysis
: May be considered in symptomatic women for 48 hours to facilitate administration of corticosteroids
Timing of Delivery
Late preterm (34 to 36+6 weeks)
delivery should be considered if there is a history of vaginal bleeding or other associated risk factors for preterm delivery.
In uncomplicated, asymptomatic women, consider delivery by Ceasarean section between
36 and 37 weeks
. Risks of bleeding, labour, or bleeding and labour requiring emergency delivery increase with advancing gestational age.
Risk factors for haemorrhage
Anterior placenta
Placenta praevia covering internal os
C/S for placenta praevia is at
increased risk of blood loss >1000mls
compared to C/S for other indications. Risk of massive haemorrhage with possibility of blood transfusion is
12 times higher
than in C/S for other indications.
Recommended anaesthesia
: Regional anaesthesia is associated with lower risks of haemorrhage compared to general anaesthesia
Blood products
: Rapid infusion and fluid warming devices should be available. Cell salvage is recommended where anticipated blood loss may induce anaemia, in particular women declining blood products.
Placenta Accreta
Antenatal diagnosis
crucial in planning management and reducing maternal morbidity and mortality
Timing of delivery
: In the absence of risk factors for preterm delivery, plan delivery between
35 and 36+6 weeks
Discuss specific risks of placenta accreta:
Massive obstetric haemorrhage, lower urinary tract damage, blood transfusion, hysterectomy, cell salvage, interventional radiological techniques
Care bundle for placenta accreta
Consultant obstetrician planning and directly supervising delivery
Consultant anaesthetist planning and directly supervising anaesthesia
Blood and blood products available
MDT involvement in pre-op planning
Discussion and consent regarding possible interventions: Leaving placenta in-situ, hysterectomy, interventional radiology, cell salvage
Local availability of level 2 critical care bed
Expectant management
Leaving the placenta-insitu may be considered if elective peripartum hysterectomy is unacceptable
Regular review, ultrasound, and access to emergency care is required
DO NOT use methotrexate
Warn patients of risk of chronic bleeding, sepsis, peritonitis, uterine necrosis, fistula, injury to adjacent organs, pulmonary oedema, renal failure, venous thromboembolism
Undiagnosed or unsuspected placenta accreta
Delay Caesarean section until appropriate staff and resources available, or arrange urgent transfer.
If placenta fails to separate, leave in-situ and proceed to hysterectomy. Attempts at removal can lead to massive haemorrhage, high maternal morbidity, and possible death.
Surgical Approach
Placenta Praevia
Consider
vertical skin and/or uterine incisions
when in transverse lie to avoid the placenta, especially below 28 weeks
Consider
pre-op and/or intra-op ultrasound
to precisely determine placental location and optimal place for uterine incision
If the placenta is transacted during uterine incision,
clamp the cord immediately
following fetal delivery to avoid excessive fetal blood loss
If pharmacological measures fail to control haemorrhage, initiate
intrauterine tamponade and/or surgical haemostatic techniques
quickly.
Interventional radiological techniques
should be employed where possible.
Early recourse to
hysterecomy
if conservative medical and surgical interventions are ineffective.
Placenta Accreta
Caesarean section hysterectomy with the placenta left in-situ
is preferable to attempting separation from the uterine wall
When the extent of the placenta accreta is limited in depth and surface area, and the entire placental implantation area is accessible and visualised (completely anterior, fundal, or posterior without deep pelvic invasion), uterus preserving surgery may be appropriate, including partial myometrial resection
Pre-operative cystoscopy and the placement of ureteric stents is recommended when the urinary bladder is invaded by placental tissue
Limited evidence to support uterus-preserving surgery in percreta and women should be informed of high risk of peripartum complications including need for secondary hysterectomy
Risk of Emergent Bleed with Placenta Praevia
35 weeks: 4.7%
36 weeks: 15%
37 weeks: 30%
38 weeks: 59%