Prenatal diagnosis of cystic fibrosis: ultrasonography of the gallbladder at 17-19 weeks of gestation.
We have investigated the ultrasonographic signs that can help in the prenatal diagnosis of cystic fibrosis in 197 risk fetuses and compared them with 353 control fetuses. In 60 fetuses with a 1:4 risk for the disease, the gallbladder was also examined. All ultrasonograms were performed just before amniocentesis at 17-19 weeks of gestation. A previously described intra-abdominal hyperechogenic mass was found in 73% of the 48 affected fetuses, but 32 of the 149 unaffected fetuses also had this feature, giving a specificity of 77% and a sensitivity of 78%. When we investigated the gallbladder, we found 9 of the 12 affected fetuses to be without evidence of a gallbladder during the sonographic examination (none of the healthy or control fetuses had such a feature), giving a positive predictive value of 100%, a specificity of 100% and a sensitivity of 75%. The combined presence of an abnormal gallbladder and a hyperechogenic intra-abdominal mass yields the same positive predictive value and specificity, but does not improve the accuracy. Ultrasonography appears to be a good additional diagnostic tool for the prenatal diagnosis of cystic fibrosis, especially when the enzyme activities disagree. Furthermore, these results lead us to think that such a finding during routine ultrasonographic examination at 17-29 weeks could be a means of screening for cystic fibrosis. The absence of the gallbladder during the sonographic examination of fetuses at risk for cystic fibrosis at 17-19 weeks of gestation can help in the prenatal detection of the disease.