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 sensivity 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.
Meconium ileus was the presenting feature of cystic fibrosis in 46 per cent of the couples which have been referred for prenatal diagnosis. In fetuses which have been aborted on the basis of alkaline phosphatase isoenzymes assays, meconium ileus represented the only pathological feature of cystic fibrosis, and was observed in three fourths of the cases. Real-time sonographic examination of fetuses at the time of amniocentesis was able to show an echogenic mass in the abdomen corresponding to the meconium ileus, and thus may afford a complementary means of diagnosis.
Prenatal diagnosis of cystic fibrosis was performed in 200 pregnancies with a 1-in-4 risk, and was based on significant modifications in amniotic fluid taken at 17, 18, 19 weeks of pregnancy, of six enzymatic assays: gamma-glutamyl-transpeptidase, aminopeptidase M, and alkaline phosphatase (total and isoenzymes). On the basis of normal values, normal outcome was predicted in 135 pregnancies reaching term, all the babies were normal. On the basis of significantly abnormal enzymatic values, an affected fetus was predicted in 56 pregnancies, 53 were terminated, and 3 went to term; the infants were affected. There were discrepancies in enzymatic values in nine cases, in eight cases normal outcome was predicted, six babies were normal and two were affected; in one case an affected baby was predicted, the pregnancy went to term and the baby is normal. Criteria giving evidence for cystic fibrosis in fetuses have been described: macroscopic observation of a typical meconium ileus, significant increase of albumin content in the meconium, and PAS-positive mucus-like material in some pancreatic acini. Using these criteria, diagnosis of cystic fibrosis has been confirmed in all the examined fetuses. The recurrence rate of cystic fibrosis was 22.5% in 147 diagnoses in which the index case had cystic fibrosis without a history of meconium ileus at birth, but was 47.5% when the index case had meconium ileus. The results of the study suggest that prenatal diagnosis of cystic fibrosis can be performed with an accuracy of 98%.
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