Tongsong T, Wanapirak C, Sirichotiyakul S
Department of Obstetrics and Gynecology, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand.
Prenat Diagn. 1999 Nov;19(11):1027-30.
The measurement of placental thickness can effectively differentiate normal pregnancies from affected pregnancies requiring invasive work-up. The objective was to evaluate the efficacy of placental thickness at mid-pregnancy in predicting fetal Hb Bart's disease in pregnancies at risk. Among 17 254 pregnant women screened for severe thalassaemia between June 1994 and December 1998, 345 pregnancies at risk for having a fetus with Hb Bart's disease underwent ultrasound examinations and cordocentesis at 18-21 gestational weeks. Before cordocentesis, the placental thickness was measured and recorded. The definite fetal diagnosis was performed with high performance liquid chromatography. The efficacy of placental thickness in predicting Hb Bart's disease was evaluated by sensitivity and specificity. Various cut-off values of the placental thickness were used for calculation and the best cut-off value was determined by a receiver-operating characteristic (ROC) curve. Of 345 pregnancies at risk, 70 fetuses with Hb Bart's disease were finally diagnosed. The mean placental thickness (+/-SD) of the normal pregnancies and pregnancies with Hb Bart's fetuses were significantly different, 24.6+/-5.2 mm and 34. 5+/-6.7 mm, respectively (Student's t-test, p<0.001). The sensitivity and specificity of placental thickness in prediction were calculated for various cut-off values. Based on the ROC curve, the best cut-off value was 30 mm (>30 mm considered abnormal), giving a sensitivity of 88.57 per cent, specificity of 90.18 per cent, positive-predictive value of 78.48 per cent and negative-predictive value of 96.87 per cent. For couples at risk, when sonographic placental thickness is normal, the risk of having an Hb Bart's fetus is markedly decreased. The measurement of placental thickness can effectively, though not absolutely, differentiate the normal pregnancies from affected ones requiring invasive work-up.
测量胎盘厚度可有效区分正常妊娠与需要进行侵入性检查的患病妊娠。目的是评估孕中期胎盘厚度对预测有风险妊娠中胎儿血红蛋白Bart病的有效性。在1994年6月至1998年12月期间接受严重地中海贫血筛查的17254名孕妇中，345例有胎儿患血红蛋白Bart病风险的妊娠在孕18 - 21周时接受了超声检查和脐带穿刺术。在脐带穿刺术前，测量并记录胎盘厚度。采用高效液相色谱法进行明确的胎儿诊断。通过敏感性和特异性评估胎盘厚度预测血红蛋白Bart病的有效性。使用不同的胎盘厚度临界值进行计算，并通过受试者操作特征（ROC）曲线确定最佳临界值。在345例有风险的妊娠中，最终诊断出70例胎儿患有血红蛋白Bart病。正常妊娠和胎儿患有血红蛋白Bart病的妊娠的平均胎盘厚度（±标准差）有显著差异，分别为24.6±5.2mm和34.5±6.7mm（学生t检验，p<0.001）。针对不同的临界值计算了胎盘厚度预测的敏感性和特异性。根据ROC曲线，最佳临界值为30mm（>30mm视为异常），敏感性为88.57%，特异性为90.18%，阳性预测值为78.48%，阴性预测值为96.87%。对于有风险的夫妇，当超声检查胎盘厚度正常时，怀有血红蛋白Bart胎儿的风险显著降低。测量胎盘厚度虽不能绝对但可有效区分正常妊娠与需要进行侵入性检查的患病妊娠。
