Contents hide

Physical Features Detected in Ultrasounds

Down syndrome is a genetic condition caused by an extra copy of chromosome 21.

This chromosomal abnormality can lead to a range of physical and developmental challenges.

Signs of Down syndrome during pregnancy can be detected during pregnancy through prenatal screening tests, such as the quadruple marker test, ultrasound scans, and amniocentesis (a procedure that analyzes fetal chromosomes in the amniotic fluid), which can help identify possible cases of Down syndrome in developing fetuses.

These tests look for specific signs, including increased Nuchal translucency on ultrasound, abnormal hormone levels in the mother’s blood, and the extra copy of chromosome 21 in the fetus.

Prenatal Screening and Diagnosis

Signs of down syndrome during pregnancy can be detected by performing a set of tests that include blood tests and ultrasound examinations.

If these signs are positive, confirmatory tests can be performed, such as chorionic villus sampling (CVS) or amniocentesis for fetal chromosomes.

The initial tests for pregnant women include the first trimester combined test and the integrated screening test. They are performed as follows:

The first trimester combined test

This is a test of the mother’s blood to measure the level of pregnancy-associated plasma protein-A (PAPP-A) and a test for the pregnancy hormone known as human chorionic gonadotropin (HCG).

Higher levels of the test than normal, indicate the possibility that the fetus suffers from Down syndrome.

Nuchal translucency screening test

This is performed by ultrasound examination, where the fetus who suffered from Down syndrome shows a collection of fluid in the tissues of the neck.

The integrated screening test

It is performed in two stages as follows:

The first trimester of pregnancy: A blood test is performed to measure PAPP-A and an ultrasound to measure nuchal translucency.
The second trimester of pregnancy: The fourth test is performed and includes alpha fetoprotein, estriol, HCG and inhibin A.

Genetic testing of the fetus

Cell-free DNA testing
Chorionic villus sampling (CVS).
Amniocentesis.
Percutaneous umbilical blood sampling (PUBS). (NIH, 2023).

Physical Features Detected in Ultrasounds

Ultrasound examination may reveal the following features of a fetus with Down syndrome:

Nuchal translucency (NT): Fluid accumulates in the tissues of the neck
Nasal bone: One of the signs that distinguishes Gowan syndrome is a missing or underdeveloped nasal bone.
Short femur: Short femur is seen in fetuses with Down syndrome.
Echogenic bowel: The intestines of a fetus with Down syndrome usually have an abnormally bright appearance.
Cardiac defects: Half of fetuses with Down syndrome have heart defects.
Facial features: Which appear flat with a small nose and upward-slanting eyes on a 3D ultrasound examination. (PubMed, 1999)

Genetic Testing for Down Syndrome

Genetic testing of embryos is performed to confirm the presence of an extra chromosome 21 through the following:

Cell-free DNA (cfDNA) test: which is a test to search for any trace of chromosome 21 in a sample of the mother’s blood and can be performed after the tenth week of pregnancy.
Amniocentesis: A sample of amniotic fluid is taken from the mother’s uterus during the period between weeks 14 and 18, where the fetal cells are isolated, cultured, and the chromosomes are examined.
Chorionic villus sampling (CVS): A sample taken from the placenta in the period between weeks 9 and 11 of pregnancy.
Percutaneous umbilical blood sampling (PUBS): A blood sample taken from the fetus’s umbilical cord during the period between weeks 18 and 22 of pregnancy.