Comparison of transabdominal and transvaginal sonography in
the diagnosis of placenta previa
Department of Obstetrics and Gynecology,
Faculty of Medicine, Prince of Songkla
University, Songkhla 90110, Thailand
Chusana Petpichetchian, Department of
Obstetrics and Gynecology, Faculty of
Medicine, Prince of Songkla University,
Purpose: To compare the accuracies of transabdominal sonography (TAS) and transvaginal sonog-
raphy (TVS) in the diagnosis of placenta previa.
Methods: A prospective, cross-sectional study was conducted at a university hospital. Both TAS
and TVS were performed on 81 pregnant women with a suspicion of placenta previa in the third
trimester. The final diagnosis was confirmed at delivery. The agreement between the two ultra-
sound methods and the parameters of each method were calculated.
Results: Fifty-eight percent of the women had a placenta previa. The sensitivities of TAS and TVS
were 86% (95% CI 78-94%) and 95% (95% CI 91-100%), respectively (p5 0.2). The specificity of
both methods was 93% (95 CI 88-99%), and the overall accuracies of TAS and TVS were 89%
(95% CI 82-96%) and 94% (95% CI 89-100%), respectively. When TAS was followed by TVS, 23%
of the previous diagnoses were changed. The agreement between both methods was good (Kappa
value 5 0.7, 95%CI 0.55-0.86).
Conclusions: For the diagnosis of placenta previa, TAS showed a high sensitivity and specificity,
which were comparable to those of TVS
Obstetrics, placenta previa, sonography
Placenta previa (PP) is a condition in which the placenta is abnormally
implanted over or within 2 cm from the internal cervical os.
weeks of gestation, the incidence of PP diagnosed by sonography (US)
has been reported to be approximately 20%. Then, it decreased to only
0.4-0.5% at term.
Accurate diagnosis of PP is important in order to
plan for prevention of fetal and maternal morbidity and mortality.
Placenta localization with transabdominal sonography (TAS) has
been a standard practice for a long time. Despite its availability and
noninvasive nature, accuracy of TAS may be limited by many factors,
such as the posterior implantation of placenta, being obscured by the
fetal head, an under-filled or over-distended bladder, the presence of
blood clots, fibroids, uterine contractions, and obesity.
tions are overcome by transvaginal sonography (TVS), which provides a
better resolution by using a higher frequency transducer, shorter
distance from the transducer to the internal os, and is not affected by
the over- or under-filling of the bladder.
TVS has been recommended by many authors as the gold standard
test for the diagnosis of PP.
At some primary care facilities, expe-
rienced obstetricians and convenient facilities may not be readily avail-
able to perform TVS. This situation is particularly common in
developing countries where TAS is available in most hospitals but
access to TVS is limited.
Most of the previous reports compared accuracy of TAS and TVS
in the diagnosis of PP based on the results from different studies. One
study that directly compared the two methods in 1999 showed better
sensitivity with TAS, but TVS was superior in overall accuracy.
in 2007 found TVS to be more accurate in measuring the placenta-to-
os distance, which helped in selecting the route for delivery.
New technology in sonography has improved imaging quality. We
considered that with appropriate selection of cases, TAS could yield
2018 Wiley Periodicals, Inc. wileyonlinelibrary.com/journal/jcu J Clin Ultrasound. 2018;46:386–390.
Received: 14 December 2017
Revised: 27 February 2018
Accepted: 12 April 2018