Case History
Recall that Shonda is at 12 weeks gestation in her first pregnancy. She doesn't know her family medical history or ancestry. Shonda is interested in conditions for which early intervention is available. The father of the baby is involved.
Question
After some discussion with Shonda, she decides she would like carrier screening, but only for conditions that are treatable. You select a laboratory that allows you to opt out of analysis for certain categories of disease, such as untreatable severe conditions, mild conditions, and adult onset conditions. The result is negative for all conditions.
What can you tell Shonda about her result?
Answer Summary
C. Her baby is at lower risk for the diseases tested, and review routine perinatal screening.
Shonda's negative result is reassuring, and her baby is at lower risk for the conditions included on the ECS. However, like any screening test, ECS does not completely rule out genetic disease for the following reasons:
- Carrier screening does not test for all genetic conditions, such as common chromosome abnormalities
- The results were limited to the conditions that you and Shonda chose to include on the screen
- Certain rare variants may not have been detected by the chosen testing technology
- No currently available test can detect all disease-causing genetic variants
Testing platforms differ in terms of the clinical sensitivity (i.e., detection rate) for specific diseases. Many laboratories will provide a statistical estimate of the remaining chance that Shonda is a carrier in light of her negative screen, called "residual risk". A genetic expert can also help you determine residual risk. These calculations are based on approximate carrier rates in the general population or specific ethnic groups. Therefore, residual risk estimates may not be available when a condition is very rare or the patient's ancestry is unknown. In Shonda's case, the result is still reassuring, but the degree of reassurance is undefined.
Despite Shonda's residual carrier risk, testing the father is not typically necessary because the remaining risk is so low. However, additional screening, such as ultrasound exam, maternal serum screening, aneuploidy screening, and newborn screening, may identify other findings suggestive of genetic conditions. Such findings may contradict her ECS results, or suggest different genetic concerns that were not assessed by ECS. Since Shonda had very specific ideas about the kind of information she wanted to learn in her pregnancy, it may be important to compare and contrast ECS with other routine pregnancy and newborn screening options.