Does having soft marker mean my baby has Down syndrome or another chromosome con

[Anonymous]

Does having a soft marker mean my baby has Down syndrome or another chromosome condition?

[Genetic Counselor]

This is one of the most misunderstood parts of prenatal ultrasound, so it is worth explaining carefully.
Soft markers were first studied in the 1980s and 1990s, before accurate blood-based screening existed. At that time, doctors were looking for any additional clue, however small, that might help identify pregnancies at higher chance for a chromosome condition. Researchers found that certain markers appeared slightly more often, as a group, among pregnancies later confirmed to involve an extra chromosome. This gave rise to the concept of a “likelihood ratio,” a number describing how much a finding should shift your estimated chance up or down from your starting-point risk.

The trouble is that these likelihood ratios vary enormously between different studies and different markers, and, more importantly, the tools available today for estimating aneuploidy chance are far more accurate than ultrasound appearance alone. Cell-free DNA screening, a blood test that analyzes small fragments of placental DNA circulating in the pregnant person’s bloodstream, correctly identifies the great majority of pregnancies affected by trisomy 21, 18, or 13, and correctly clears the great majority that are not affected. Because this blood test is so accurate, current guidelines from ACOG and SMFM state plainly that when a soft marker is found in a pregnancy that has already had a negative cell-free DNA or serum screening result, the marker does not meaningfully change that low chance, and additional invasive testing is not recommended for that reason alone.

No. Having a soft marker does not mean your baby has a chromosome condition, and for most soft markers, most of the time, it does not meaningfully raise your baby’s individual chance either.

Two markers deserve a specific mention because their story is a little different from the rest. Choroid plexus cysts and echogenic intracardiac foci were historically associated mainly with trisomy 18 and trisomy 21 respectively, but when they occur as truly isolated findings, meaning no other structural or genetic concern is present, current evidence shows they add very little useful information once modern screening has already been done. Echogenic bowel is somewhat different again: while it is included among the soft markers for chromosome conditions, it has also been associated with a handful of other, non-chromosomal conditions, including cystic fibrosis and, less commonly, an infection acquired during pregnancy or a problem with fetal growth, which is one reason it is evaluated a little more thoroughly than some other markers, independent of aneuploidy risk.

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