TRANSLABIAL ULTRASOUND IN PLACENTA PREVIA

Translabial ultrasound is an effective and accepted method for assessing the low-lying placenta in the third trimester.

Translabial ultrasound has been proved to be superior to the transabdominal route (1). It is less invasive than transvaginal ultrasound and can effectively demonstrate the internal os and endocervical canal when these structures are obscured on transabdominal scanning (especially when the fetal head is low in the lower uterine segment).

TECHNIQUE

(as described by Jeanty and co-workers) (2)

• 3.5 MHz electronic array transducer (covered with a plastic sheath).
• Patient supine with hips abducted.
• Scan head is placed between the labia majora anterior to the vaginal introitus, and is orientated along the axis of the vagina.

ULTRASOUND

• Placental tissue completely covered the internal cervical os.
• Placental tissue partially covers the internal os.
• Distance measured between the internal os and margin of the placenta.
  If over 2-3 cm = marginal, and vaginal delivery is reportedly safe (1).
• When the distance is less than 1cm, cesarean section is recommended.

REFERENCES

1. Dawson WB, Dumas MD, Romano WM et.al. Translabial ultrasonography and placenta previa: Does measurement of the os-placenta distance predict outcome. J Ultrasound Med 1996;15:441-446.
2. Jeanty P, d'Alton M, Romero R et.al. Perineal scanning. Am J Perinatol 1986;3:289.