Does second trimester screening result “high risk” mean for Down syndrome?

[Anonymous]

My second trimester screening result is “high risk” for Down syndrome. Does this mean my baby has a genetic condition, and what happens next?

[Genetic Counselor]

No. A high-risk result means the chance is higher than the laboratory’s cut-off. It does not mean the baby has the condition. Because the test flags about 5 in every 100 pregnancies, and Down syndrome is much less common than that, most pregnancies with a high-risk result turn out to have a baby with normal chromosomes. Your exact number matters. A result of 1-in-20 is very different from a result of 1-in-200.
It is natural to feel worried. Because this result comes later in pregnancy, it helps to take the next steps without delay, so you have enough time to think and decide.

• Meet a genetic counselor or clinical geneticist. They will explain what your number means, check that the pregnancy dates used in the calculation were correct, and review your family history and scan findings.
• Option 1: Non-Invasive Prenatal Testing. This blood test looks at small fragments of DNA from the placenta in the mother’s blood. It is far more accurate than the quadruple marker test for Down syndrome, Edwards syndrome, and Patau syndrome, and carries no risk to the pregnancy. It is still a screening test, so a high-risk result from it also needs confirmation. Results usually take about a week.
• Option 2: Amniocentesis. This gives a definite answer by testing the baby’s own cells from the fluid around the baby. It can be done from 15 weeks onwards, so it is the usual diagnostic test at this stage of pregnancy. The chance of miscarriage from the procedure is small, about 1 to 3 in every 1,000 in experienced hands, and should be weighed against the chance found on screening.
• What the laboratory tests for: A rapid test for the common trisomies often gives results within a few days. Full chromosome results take longer. If the anatomy scan shows a structural difference, guidelines recommend chromosomal microarray, which finds smaller missing or extra pieces of chromosomes.

Some families choose further testing to prepare for the birth. Others choose not to test at all. Both are valid choices, and your care team should support whichever path you take.

[Author]

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