Genetic evaluation of the fetus with a structural abnormality identified on ultrasound examination

Structural anatomic abnormalities identified by ultrasound are associated with an increased risk of fetal genetic abnormality. Structural anatomic abnormalities do not include soft markers, such as echogenic intracardiac focus, choroid plexus cyst, slightly short humerus or femur, thickened nuchal fold, urinary tract dilation, echogenic bowel, and absent or hypoplastic nasal bone.

CVS: chorionic villus sampling; FISH: fluorescence in situ hybridization.

* For invasive testing, CVS is offered through 14 weeks of gestation; amniocentesis is offered at 15 weeks of gestation and beyond.

¶ Offer an invasive procedure for diagnostic testing when "no result" is reported due to increased association of test failures and fetal aneuploidy.

Δ FISH test panel should include chromosomes 13, 18, 21, X, and Y. Although FISH provides a rapid result, it also adds to the cost of the fetal evaluation, so it is also reasonable to proceed directly to chromosomal microarray.

◊ The sensitivity of cell-free DNA testing is very high for the common aneuploidies, so further prenatal testing for these aneuploidies is not recommended.

§ A positive cell-free DNA screening test must be confirmed with a diagnostic test, particularly if pregnancy termination is planned based on test results.

¥ Although microarray will be abnormal if the fetus has an unbalanced translocation, a karyotype is necessary to distinguish the fetus with an unbalanced translocation inherited from a healthy carrier parent with a balanced translocation versus the fetus with a free-lying, extra chromosome from nondisjunction.

Graphic 108719 Version 6.0

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Genetic evaluation of the fetus with a structural abnormality identified on ultrasound examination