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Placenta Previa

Neelam Maurya

Placenta Previa

DEFINITION:

  • When the placenta is implanted partially or completely over the lower uterine segment (over and adjacent to the internal os) it is called placenta previa.

ETIOLOGY:

  • Multiparity
  • Increased maternal age (> 35 years)
  • History of previous cesarean section 
  • Previous placenta previa
  • Large Placental size and abnormality
  • LSCS
  • Smoking
  • Prior curettage.

TYPES OR DEGREES:

  • Type—I (Low-lying): The major part of the placenta is attached to the upper segment and only the lower margin encroaches onto the lower segment but not up to the os.
  • Type—II (Marginal): The placenta reaches the margin of the internal os but does not cover it.
  • Because of the curved birth canal major thickness of the placenta (about 2.5 cm) overlies the sacral promontory, thereby diminishing the anteroposterior diameter of the inlet and prevents engagement of the presenting part. This hinders effective compression of the separated placenta to stop bleeding. 
  • Placenta is more likely to be compressed, if vaginal delivery is allowed.
  • More chance of cord compression or cord prolapse. 
  • Type—III (Incomplete or partial central): The placenta covers the internal os partially 
  • Type—IV (Central or total): The placenta completely covers the internal os even after it is fully dilated.

CLINICAL FEATURES:

  • Vaginal bleeding:
  • Sudden onset, painless,fatal, apparently causeless and recurrent
  • Cause of inevitable bleeding:placental growth↓→ inelastic placenta is sheared off→ open up uteroplacental vessels

Mechanisms of spontaneous control:

  • Thrombosis of the open sinuses.
  • Mechanical pressure by the presenting part
  •  Placental infarction.
  • Size of the uterus is proportionate to the period of gestation.
  • Uterus :relaxed, soft and elastic without any localized area of tenderness.
  • Persistence of malpresentation like breech or transverse or unstable lie is more frequent.
  • Increased frequency of twin pregnancy
  • Premature labour 
  • Head is floating
  • Persistent displacement of the fetal head is very suggestive.
  • Head cannot be pushed down into the pelvis.
  • Fetal heart sound:Stallworthy’s sign:Slowing of the fetal heart rate on pressing the head down into  pelvis which soon recovers promptly as the pressure is released is suggestive of the presence  of low lying placenta especially of posterior type

DIAGNOSIS:

Sonography

  • Transabdominal ultrasound (TAS):after 30th week of gestation is about 98%
  • Transvaginal ultrasound (TVS):Safe, obviates the discomfort of full bladder and is more accurate (virtually 100%) than TAS
  • Transperineal ultrasound:Internal os is visualized in 97–100% of cases.
  • Color Doppler flow study
  • 3D Power Doppler study
  • Magnetic Resonance Imaging (MRI)

Clinical:

  • By internal examination
  • Direct visualization duringCS
  • Examination of the placenta following vaginal delivery
  • Per vaginal examination is contraindicated in a patient with placenta previa prior to term.

COMPLICATIONS:

MATERNAL:

During pregnacy:

  • Antepartum hemorrhage with varying degrees of shock
  • Malpresentation
  • Premature labor
  • Death due to massive hemorrhage

During labor

  • Early rupture of membranes
  • Cord prolapse
  • Slow dilatation of cervix
  • Intrapartum hemorrhage
  • Increased incidence of operative interference
  • Postpartum hemorrhage
  • Retained placenta and increased incidence of manual removal
  • Puerperium:Sepsis is increased,Subinvolution,Embolism

FETAL :

  • Low birth weight
  • Asphyxia
  • Intrauterine death
  • Birth injuries
  • Congenital malformation
  • Maternal and fetal morbidity and mortality

MANAGEMENT:

PREVENTION:

  • Adequate antenatal care
  • Antenatal diagnosis of low lying placenta at 20 weeks
  • Significance of “warning hemorrhage” should not be ignored.
  • Color flow Doppler USG in placenta previa is indicated to detect any placenta accreta

Expectant management(Macafee and Johnson method):

Selection of cases:

  • Mother is in good health status (hemoglobin > 10 g%; hematocrit > 30%).
  • Duration of pregnancy is less than 37 weeks
  •  Active vaginal bleeding is absent
  • Fetal well-being is assured (CTG and USG).
  • Carried up to 37 weeks of pregnancy.
  • Contraindicated in Active labour

Treatment:

  • Bed rest
  • Investigations
  • Periodic inspection of vulval pads and fetal surveillance with USG
  • Supplementary hematinics
  • Adequate cross matched blood transfusion
  • Speculum (Cusco’s) examination is made:2-3 days after the bleeding stops

Preterm delivery:

  • Recurrence of brisk hemorrhage
  • Dead fetus
  • Congenitally malformed fetus 
  • Steroid therapy

Active (Definite) Management (Delivery):

Cesarean delivery:

  • If placental edge is within 2 cm from the internal os
  • Central placenta previa with anencephaly fetus
  • Type IV placenta previa

Vaginal delivery: 

  • 2–3 cm away from the internal cervical os
  • Contraindicated in Central placenta previa 
Exam Question
 
  • Anti-D administration, Corticosteroids & Blood transfusion  are included in the expectant management of placenta praevia
  • In Browne’s classification of placenta previa, the placenta covers the internal os when closed but not when fully dilated is Type 3
  • The initial hemorrhage is usually painless and fatal in placenta praevia
  • Per vaginal examination is contraindicated in a patient with placenta previa prior to term.
  •  There may be torrential bleeding if PV is done in a patient with placenta previa.
  • Expectant management of placenta praevia by Macafee and Johnson method
  • Placenta previa is characterized by Painless , Causeless  & Recurrent bleeding
  • Expectant line of management in placenta previa is contraindicated in Active labour
  • Premature labour is common in placenta previa
  • The best way to diagnose the degree of placenta previa is Trans vaginal sonography
  • Placenta previa mouth is associated with Large placenta, Previous C. S. scar & Previous placenta previa
  •  Incidence increases by two fold after LSCS
  • Conservative management is contraindicated in a case of Placenta previa in Evidence of fetal distress, Fetal malformations & Women in labour
  • Termination of pregnancy in placenta previa is in­dicated in Active bleeding, active labour & Fetal malformation
  • Cesarean section is absolutely indicated in Type IV placenta previa
  • A case of central placenta previa with anencephaly fetus should be delivered by Cesarean section
  • Vaginal delivery is contraindicated in Central placenta previa
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