Management of a Low Lying Placenta Max Brinsmead MB BS PhD August 2018

Routine 2nd Trimester Ultrasound Will warn of a placenta that is implanting in the lower segment of the uterus Anatomically defined as below the peritoneal reflection from uterus to bladder Internal cervical os is the other major landmark

If the placenta reaches or covers the internal os at 20 weeks… Follow up Vaginal Ultrasound is required Because the placenta will “migrate” in up to 80% of instances of low placenta identified by routine abdominal ultrasound in the 2nd trimester But this is less likely if the placenta is posterior

If the degree of previa is minor and there is no APH… Follow up ultrasound can be deferred until 36 weeks gestation But any APH requires further immediate evaluation As does any major encroachment or “central placenta previa”

Vaginal delivery is possible If the leading placental edge is >3 cm from the internal os on vaginal ultrasound Vaginal delivery is possible Maybe even 2 cm if the placenta is anterior But major encroachment closer than 2 – 3 cm will require Caesarean delivery

Patients with Major Placenta Previa Re evaluate with vaginal ultrasound at 32 weeks Warn about risk of APH and take all suitable precautions Hospital care may be required in order to reduce risk to the mother but prolong the pregnancy as long as possible

Placental implantation extends through decidua to the myometrium Placenta Accreta Placental implantation extends through decidua to the myometrium Is more common after a previous Caesarean and with an anterior placenta previa Major haemorrhage at the time of deliver may require hysterectomy

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