Analysis of 3208 cystic fibrosis prenatal diagnoses: impact of carrier screening guidelines on distribution of indications for CFTR mutation and IVS-8 poly(T) analyses.

Purpose: To evaluate and quantify indications for CFTR mutation analysis of prenatal specimens, and to determine if a significant portion of tests are performed only for the identification of 5T alleles, we surveyed our laboratory data over a 3-year time period that spanned the issuance of the cystic fibrosis (CF) carrier screening guidelines.

Methods: Referral indications for 3208 prenatal specimens were compared for an 18-month period before (April 2000 to September 2001) and after (October 2001 to April 2003) publication of the ACMG/ACOG statement regarding prenatal and preconception testing for CF.

Results: The frequency of cases received for testing when one or both parents were CF mutation carriers did not change significantly after publication of the guidelines. The most frequent indication during the entire 3-year period was fetal ultrasound abnormality, yet in the post-ACMG/ACOG period the percentage decreased significantly due to an increase in the number of prenatal screening cases. Testing indications related to parental 5T status also increased significantly in the post-ACMG/ACOG period and accounted for 2.9% of testing over the 3-year period. A small subset (1.6%) of prenatal specimens were tested for poly(T) even though the parents did not carry 5T allele(s). However, more than 40% of these cases could be attributed to parental R117H mutations.

Conclusion: These data indicate that although indications for prenatal testing shifted after the issuance of carrier screening guidelines, prenatal testing related to parental 5T alleles comprised < 3% of the total referral indications.