Westerway Susan Campbell, Hyett Jon, Henning Pedersen Lars
Faculty of Dentistry and Health Sciences Charles Sturt University Wagga Wagga New South Wales Australia.
RPA Women and Babies Royal Prince Alfred Hospital University of Sydney Camperdown New South Wales Australia.
Australas J Ultrasound Med. 2017 Sep 15;20(4):163-167. doi: 10.1002/ajum.12065. eCollection 2017 Nov.
We aimed to compare the value of transabdominal (TA) and transvaginal (TV) approaches for assessing the risk of a low-lying placenta. This involved a comparison of TA and TV measurements between the leading placental edge and the internal cervical os. We also assessed the intra-/interobserver variation for these measurements and the efficacy of TA measures in screening for a low placenta.
Transabdominal and TV measurements of the leading placental edge to the internal cervical os were performed on 369 consecutive pregnancies of 16-41 weeks' gestation. The difference (TA-TV) from the mean was calculated and plotted against gestational age. Bland-Altman plots and paired t-tests were used to look at the differences in TA/TV measurement. Screening performance of a transabdominal approach was compared to a transvaginal 'gold standard'. Nonparametric methods were used to calculate the area under the receiver operator characteristics (ROC) curve. Intra-/interobserver variations were also calculated.
Of the pregnancies, 278 had a leading placental edge that was visible with the TV approach. Differences (TA-TV) ranged from -50 mm to +57 mm. Bland-Altman plot shows that TA measurements overestimated the distance compared with the TV measurements; the average difference in measurement was 12.0 mm (95% confidence interval 9.9-14.1). The sensitivity, specificity and negative predictive values of a TA approach were 18.2%, 97.5% and 87.2%, respectively. The receiver operator characteristics area between gestational weeks 16-23 was 0.81 (95% CI: 0.76-0.86).
The TA approach has a low sensitivity for detecting a low-lying placenta as choosing a TA cut-off with sensitivity >90% will decrease the specificity to 50%.
我们旨在比较经腹（TA）和经阴道（TV）途径评估前置胎盘风险的价值。这涉及比较TA和TV测量的胎盘前缘与宫颈内口之间的距离。我们还评估了这些测量的观察者内/间变异以及TA测量在前置胎盘筛查中的有效性。
对369例妊娠16 - 41周的连续孕妇进行经腹和经阴道测量胎盘前缘至宫颈内口的距离。计算与平均值的差值（TA - TV）并绘制与孕周的关系图。采用Bland - Altman图和配对t检验观察TA/TV测量的差异。将经腹途径的筛查性能与经阴道“金标准”进行比较。使用非参数方法计算受试者工作特征（ROC）曲线下面积。还计算了观察者内/间变异。
在这些妊娠中，278例胎盘前缘可经阴道途径观察到。差值（TA - TV）范围为 - 50 mm至 + 57 mm。Bland - Altman图显示，与经阴道测量相比，经腹测量高估了距离；测量的平均差值为12.0 mm（95%置信区间9.9 - 14.1）。经腹途径的敏感性、特异性和阴性预测值分别为18.2%、97.5%和87.2%。妊娠16 - 23周之间的受试者工作特征面积为0.81（95%CI：0.76 - 0.86）。
经腹途径检测前置胎盘的敏感性较低，因为选择敏感性>90%的经腹截断值会将特异性降低至50%。
