Placenta praevia

• Overview:

  • Occurs when the placenta lies in the lower uterine segment
  • Can lead to the complete or partial covering of the internal cervical os (endocervix)
• Classification:

  • Grade 1 - placenta encroaches the lower segment of the uterus but does not reach the internal os
  • Grade 2 - the placenta reaches the internal os but does not cover it
  • Grade 3 - the placenta partially covers the internal os but does not fully cover
  • Grade 4 - placenta completely covers the internal os
• Placenta praevia can also be grouped into two subtypes:

  • Minor placenta praevia (grade 1 and 2): the placenta is low but does not cover the internal cervical os
  • Major placenta praevia (grade 3 and 4): placenta lies over the internal cervical os
• Risk factors:

  • previous caesarean section (placenta attaches to scar)
  • Previous placenta praevia
  • Previous termination of pregnancy
  • Multiparity and multiple pregnancy
  • Advanced maternal age (over 40)
  • Smoking
  • Deficient endometrium - uterine scar
  • Assisted conception
• Investigation:

  • Typically identified at the mid pregnancy (18+6 to 21+6 weeks of gestation) USS
  • With advancing gestation the lower uterine segment grows and thins which can move the placenta upwards
  • Transvaginal scan at 32 weeks - if still present, repeat TVS at 36 weeks
  • If still present at 36 weeks - delivery via caesarean section is recommended - due to significant risk of spontaneous labour and associated haemorrhage
• Transvaginal USS:

  • More precise measurement between placenta and internal os
  • Better than transabdominal USS
  • Different classification:
  • Placenta praevia = placenta lies directly over internal os
  • Low lying placenta = placental edge is less than 20mm from the internal os
  • Normal = placental edge is 20mm or more from the internal os
• Presentation:

  • PV bleeding - can be spotting or massive haemorrhage
  • Painless (in contrast to uterine abruption)
  • Uterus soft
  • Presenting part free/high - feel baby higher due to obstructing placenta
  • Abnormal lie - including transverse
• Do not perform digital vaginal exam unless placental location known - can provoke haemorrhage
• Investigations dictated by degree of bleeding:

  • FBC
  • Clotting
  • G+S and crossmatch
  • U&Es
  • LFTs
  • If patient Rh negative - Kleihauer test (degree of foetal RBC in maternal circulation)
  • USS
  • Assessment of foetal heart rate - CTG