Translabial ultrasonography and placenta previa: does measurement of the os-placenta distance predict outcome?

Abstract

The aim of this study was to assess the value of the measurement of os-placenta distance by translabial ultrasonography in the evaluation of placenta previa. This method was used in 40 women with suspected placenta previa to measure the distance between the placenta and internal cervical os. Sonographic diagnoses were compared to placental location determined at delivery. Translabial ultrasonography proved superior to the transabdominal route in both diagnosis and exclusion of placenta previa. Measurement of the os-placenta distance can be used as an adjunct to clinical assessment to predict the likelihood of safe vaginal delivery in cases of suspected placenta previa.

Vasa previa: Prenatal diagnosis by transperineal sonography with Doppler evaluation

“…This technique is used in many clinics to visualize the cervix and to assess placental location. 17,18,21,22 The cases reported here confirm that transperineal sonography can successfully visualize blood vessels crossing the cervical os in cases of vasa previa. Confirmation that the structures crossing the os are blood vessels can be obtained with Doppler evaluation in this transperineal perspective.…”

Using ultrasound in the clinical management of placental implantation abnormalities

“…As compared to those with cervical os to placental edge distance between 11-20 mm, patients with internal cervical os to placental edge distance 10 mm have high rates of antepartum hemorrhage (29% vs 3%; odds ratio, 11.5; 95% confidence interval, 1.6e76.7) 13 and cesarean delivery rates 73-91% vs 24-40%. 10,13,14 However, there are no significant differences in the gestational ages at delivery between the 2 groups and 75-80% of these patients are delivered at term. 13 The thickness of the lower placental edge has also been evaluated as a predictor of bleeding in patients with marginal/low-lying placentas.…”

“…20 In women with low-lying placenta (cervical os to placental edge distance 20 mm), cervical length has been studied as a predictor of antepartum bleeding and indicated preterm birth. 10,[12][13][14] It was found that short cervix ( 25 mm) was associated with higher rates of antepartum bleeding (75% vs 31%; P ¼ .02), blood transfusion (25% vs 3%; P ¼ .02), lower birthweight (62% vs 17%; P ¼ .02), and neonatal intensive care unit admissions (50% vs 17%; P ¼ .04). 22 Figure 3 is a proposed guideline for managing asymptomatic patients with marginal or low-lying placenta based on published literature that has used internal cervical os to placental edge distance cutoffs of <1, 1-2, and >2 cm; placental edge thickness cutoff of 1 cm; and cervical length cutoff of 25 mm.…”

“…[9][10][11][12][13][14]22,23 If the distance between the internal cervical os and the placental edge is >20 mm, the patients should be managed as per routine because the overwhelming majority of studies have not demonstrated an increased risk for cesarean delivery due to hemorrhage. [9][10][11][12][13] Due to the normal process of "placental migration" as the lower uterine segment matures, the ultrasound examination may be repeated in the third trimester to identify those patients who can be allowed to go to term vs those who are at increased risk for antepartum hemorrhage and preterm delivery, and therefore need to be carefully watched. Useful ultrasound parameters include: (1) the distance itself between the internal cervical os and the placental edge (<10 vs 10-20 mm); Antepartum management of placenta previa (with or without accreta) Antepartum management of asymptomatic patients with suspected placenta previa (with or without placenta accreta) at second-trimester ultrasound screening examination.…”

Diagnosis and management of placenta previa

“…Transperineal or translabial ultrasound (using a transabdominal probe) can also improve upon the diagnostic accuracy of TAS and may be a useful alternative when TVS is not available [29].…”