Prenatal Diagnosis
Definition
Tests performed before birth to detect changes in the fetus's genes or chromosomes.
Purpose
Offered when the risk of a genetic or chromosomal condition is increased; it helps reduce uncertainty and supports decision-making.
Results
Prenatal tests fall into two groups, and this distinction determines how the result is interpreted:
| Screening | Diagnosis | |
|---|---|---|
| What it tells | Whether the risk is higher than average | Whether the condition is present |
| Example | NIPT, double/triple screening | Amniocentesis, CVS |
| Procedure | Blood draw from the mother | Sampling with a needle |
| If positive | Confirmation required | Confirmation not required |
A positive screening result is not a diagnosis. It only shows that the risk is higher than average; a confirmatory diagnostic test is required for a definitive answer.
Risks and Limitations
Prenatal testing cannot detect all hereditary diseases and birth defects. A normal result does not mean the baby will have no health problems.
Invasive diagnostic tests (amniocentesis, CVS) carry a low, though nonzero, level of risk. The decision to have the test is personal; genetic counseling helps in making this decision.