Screening for cystic fibrosis (CF) is common in Western countries before pregnancy to assess the risk of having a child with CF. Most tests focus only on common mutations. This study shows that these targeted approaches are less effective for people of non-European ancestry, particularly those of South Asian descent. It also reveals that some tests include mutations with variable effects while others do not, and this choice influences claims about test accuracy. The findings highlight how the choice of testing method affects effectiveness across ancestries, raising important questions about equity in genetic testing. (By Eric Lee, https://jmg.bmj.com/content/early/2024/12/31/jmg-2024-110365 )