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4.2.4 Low-lying Placenta and Placenta Previa

Low-Lying Placenta Definition

The placental edge does not cover the cervical os but lies ≤ 20mm from the os. 

Placenta Previa Definition

The internal cervical os is covered partially or completely by the placenta.

Risk Factors for Placenta Previa

  • Maternal age  (>35 years of age)​
  • Multiparity​
  • Cigarette smoking​
  • Uterine leiomyomas ​
  • Prior cesarean deliveries​
  • Elevated maternal serum AFP levels (not otherwise explained)​
  • Assisted reproductive technology​
  • Multi-fetal gestation​

Pre-operative Management of Low-lying placenta and Placenta Previa​

  • In patients with a low-lying placenta, a recent ultrasound (within 7-14 days) should be used to confirm placental location prior to Caesarean delivery.​
  • In women with placenta previa or low-lying placenta and in the presence of risk factors or limited access to urgent obstetrical care, consider in-hospital management.​

Clinical Pearl

Typically patients are not admitted unless there is an antepartum hemorrhage. Approximately 30% of patients will not experience bleeding so are managed as an outpatient. If there is a bleed, generally it is self-limiting so there should be time to transfer the patient out. It would be unusual for bleeding to be so severe that immediate delivery would be necessary.

  • Administer antenatal corticosteroids for potential preterm delivery only if the risk of delivery within 7 days is very high and not solely because admission to the hospital is deemed necessary.​
  • Tocolysis can be considered in women with antepartum hemorrhage associated with uterine contractions in order to allow administration of corticosteroids or transfer of care, but not for prolongation of pregnancy.​

Clinical Pearl

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In a rural setting, after one significant bleed (after viability), if concerns about abnormal placentation exist, transfer out is reasonable. The natural course of placenta previa is that after a sentinel bleed, there is increased risk for recurrent bleeds becoming heavier and more frequent as term is approached.

Timing of Delivery

  • Cesarean delivery is recommended in women with a low-lying placenta with the placental edge ≤10 mm from the cervical os at 37+0 to 37+6 weeks gestation in the presence of risk factors and at 38+0 to 38+6 weeks gestation in the absence of risk factors.​
  • A trial of labour is recommended in women with a low-lying placenta where the placental edge is 11 to 20 mm from the cervical os and can be considered in carefully selected women where the placental edge is ≤10 mm from the cervical os.​

Clinical Pearl

For patient who has had an antepartum bleed in the context of a low-lying placenta or previa, delivery would generally be planned between 36 to 36+6 weeks.

Surgical Considerations

Preparation

  • Regional anaesthesia is safe and adequate as a first-line anaesthetic approach for the peripartum management of patients with placenta previa or low-lying placenta.​
  • 2-4 units pRBC should be made available​
  • Appropriate surgical instruments to perform a Caesarean hysterectomy should be on-hand (insert link to C-hyst module)​
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Clinical Pearl

Have a pre-operative anaesthesia consult done. Insert 2 large bore IVs. Have an experienced assist. Have uterotonics, a Bakri balloon, and other hemostatic agents on-hand and at the ready!

​Managing the Placenta

  • Attempt to avoid disrupting the placenta upon hysterotomy. If the placenta is incised, fetal hemorrhage can occur, so fetal delivery and cord clamping should be undertaken rapidly.​
  • If placenta is anterolateral, a vertical incision may be used on the contralateral side of the lower segment.​
  • If placenta wraps around the cervix from anterior to posterior in the midline, a transverse or vertical incision may be possible above it though can lead to extensions into the upper segment.​
  • Following placental removal, the placental site may bleed uncontrollably due to poorly contracted smooth muscle in the lower uterine segment, but may also be the result of focal placenta accreta.​

Clinical Pearl

Point of care ultrasound can be useful to help see the edge of the placenta. You can use a sterile U/S probe cover and ultrasound directly on the uterus to identify the edge of the placenta. 

Clinical Pearl #2: Occasionally a midline skin incision is used to have enough access to avoid the placenta (ie. In accreta cases)

  • Attempt to avoid disrupting the placenta upon hysterotomy. If the placenta is incised, fetal hemorrhage can occur, so fetal delivery and cord clamping should be undertaken rapidly.​
  • If placenta is anterolateral, a vertical incision may be used on the contralateral side of the lower segment.​
  • If placenta wraps around the cervix from anterior to posterior in the midline, a transverse or vertical incision may be possible above it though can lead to extensions into the upper segment.​
  • Following placental removal, the placental site may bleed uncontrollably due to poorly contracted smooth muscle in the lower uterine segment, but may also be the result of focal placenta accreta.​

Hemostasis

1. Administer uterotonics and TXA and apply temporizing measures. ​

  • TXA​
  • Oxytocin​
  • Carbetocin​
  • Ergot​
  • Hemabate​
  • Apply direct pressure to the placental bed​
  • Tourniquets have been suggested as a temporizing measure – use a bladder catheter or Penrose drain tied tightly around the lower segment of the uterus to occlude the uterine vessels then secure with a clamp.

Clinical Pearl

Exteriorizing the uterus can be helpful for visualization, manual compression, and allowing for enough time for assists/instruments/medications to work!​

2. Treat focal bleeding

  • Oversew the placental bed with compression square sutures​
  • Make four to six 2 by 2 cm squares in the area of placental bed bleeding using 1-0 Vicryl. Sutures should penetrate the decidua and extend into the myometrium but not beyond the uterine serosa. The ends of the sutures are tied down tightly to compress the enclosed vessels.​
  • Place fibrin patch or glue​
  • Apply Monsel’s solution​
  • Placental site injection of vasopressin​
  • 4-5 units in 20cc of NS injected into the site in 1-2mLs​
  • Excise the area, if small and accessible – this may be particularly helpful in cases of focal placenta accreta​

Clinical Pearl

Let anaesthesia know any time you are injecting vasopressin, and ensure it is not intravascular. By the time you are considering vasopressin, however, you should be moving towards compression sutures!

3. Ligation of uterine and utero-ovarian arteries (O’Leary stitch).​

  • Identify the ureters.​
  • Using 0 Vicryl on a large curved needle, pass the stitch through the lateral aspect of the uterine segment close to the cervix then back through the broad ligament lateral to the vessels.​
  • If this fails, ligate the vessels of the utero-ovarian arcade distal to the cornua by suturing through the myometrium medial to the vessels, back through the broad ligament lateral to the vessels, and tying for compression. 

 4. Intrauterine tamponade or compression sutures

  • Insert a Bakri balloon (link to module)
  • If the Bakri fails, deflate the balloon and
  • apply a B-Lynch compression suture.
  • Then close hysterotomy.
  • Re-inflate the balloon catheter while observing the myometrium and stopping filling before blanching occurs at the suture sites.

Clinical Pearl

Bakri balloons can be placed through the
hysterotomy and passed to an assist who receives the end
through the vagina. Alternatively, they can be placed vaginally
by an assist!

5. Refractory Bleeding

  • If uterine artery embolization is available rapidly by Interventional Radiology, this may be considered.
  • Internal iliac ligation (consider if Vascular Sx or Gen Sx available)
  • Hysterectomy

Clinical Pearl

Postpartum bleeding is almost always a surgical problem, and
medical management can be considered, but IR is most often applicable in the
post-hysterectomy cases.

Updated on June 28, 2021

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