Non-invasive prenatal diagnosis for a single-gene condition looks for a specific variant. If the variant in the affected relative or carrier parents is not already known, the test cannot be designed in time to be useful in that pregnancy. When a couple has an affected child or a family history of a condition such as thalassaemia, cystic fibrosis or spinal muscular atrophy, confirm the family's variant and parental carrier status before or very early in pregnancy, and refer to clinical genetics.
- Ask about affected relatives and prior affected children at booking.
- Confirm the family's pathogenic variant from the relative's records or a genetics report.
- Arrange parental carrier testing before or early in pregnancy, not at the anomaly scan.
- Refer to clinical genetics as soon as a familial single-gene condition is identified.
Why it matters
Every week lost to finding the family variant narrows the couple's options in that pregnancy.
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