Predicting the risk of cystic fibrosis with echogenic fetal bowel and one cystic fibrosis mutation

Objective: To assess fetal risk for cystic fibrosis when echogenic bowel an d one cystic fibrosis mutation are detected. Methods: A hypothetical cohort of 1000 women with singleton pregnancies and echogenic fetal bowel during the second trimester was used to determine th e probability of cystic fibrosis when one cystic fibrosis transmembrane con ductance regulator mutation was detect-ed. The risk of cystic fibrosis was calculated using the range of prevalence of cystic fibrosis in fetuses with echogenic bowel reported in the literature. Risk calculations for fetuses of Ashkenazi Jewish, Northern European, African-American, Hispanic, and Asi an descent accounted for carrier frequencies and mutation detection rates s pecific to each ethnic group. Results: As the assumed prevalence of cystic fibrosis increases from 1-25%, the probability that a white fetus with one mutation and echogenic fetal b owel actually has cystic fibrosis increases from 4.8% to 62.5%. Assuming a 2% risk of cystic fibrosis with echogenic fetal bowel, an Ashkenazi Jewish fetus and an Asian fetus with echogenic bowel and one mutation have a 3.1% and 72% risk of cystic fibrosis, respectively. The probability of cystic fi brosis in a nonwhite fetus is between those two extremes. Conclusion: The probability of cystic fibrosis after detection of echogenic bowel and one cystic fibrosis mutation varied among ethnic groups. Even at the highest prevalence of cystic fibrosis, most white fetuses will not hav e cystic fibrosis. In nonwhite populations almost half of these fetuses wil l have cystic fibrosis, even at the lowest prevalence of cystic fibrosis. ( Obstet Gynecol 1999;94:1020-3. (C) 1999 by The American College of Obstetri cians and Gynecologists.).