Signs of Trisomy 21 During Pregnancy

What is trisomy 21?

Often known as Down syndrome, it is a genetic condition resulting from an extra copy of chromosome 21, instead of the usual pair. This genetic condition (aneuploidy) can lead to developmental delays, both motor and mental, as well as changes in body and facial structure.

This aneuploidy can be detected by ultrasound in combination with specific biochemical markers through prenatal screening, beginning in the first trimester.

This evaluation allows for proper monitoring of the baby’s health and provides support and guidance to parents throughout the entire pregnancy.

Prevalence of Trisomy 21

This syndrome is common, as one in every 700 newborns will have the condition; it can occur at any age but is more common when mothers are over 40.

Understanding the importance of the risk factors associated with the syndrome highlights the need for medical care and monitoring, including the early detection of signs of trisomy 21 during pregnancy.

Prenatal Diagnosis: Why Is It Important?

Prenatal Diagnosis—First-Trimester Combined Screening—is a crucial and fundamental test designed to assess the risk of trisomy 21 in the fetus, as well as the presence of other chromosomal disorders, such as trisomy 18 (Edwards syndrome) or trisomy 13 (Patau syndrome).

This screening is crucial for identifying the likelihood of trisomy 21 in the fetus, allowing healthcare professionals to make more informed decisions and provide personalized care tailored to the needs of the mother and baby.

When should the screening be performed?

To identify signs of trisomy 21 during pregnancy, it is recommended that the First-Trimester Combined Screening be performed between the 10th and 13th week plus 6 days of gestation, calculated from the date of the last menstrual period.

Since it is not a diagnostic test in and of itself, it does not completely rule out the possibility that the baby has Down syndrome, Edwards syndrome, or Patau syndrome, nor does it entirely eliminate the possibility of birth defects or other conditions that cannot be detected by prenatal screening.

How Is Prenatal Diagnosis Performed?

After screening, if signs of trisomy 21 are identified during pregnancy, invasive diagnostic methods may be used, such as chorionic villus sampling (CVS) or amniocentesis, which allow for the collection of cells from the baby, providing a definitive diagnosis.

However, it is important to note that these procedures carry a risk of miscarriage (0.5 to 1%), which is why it is important to undergo prenatal screening before proceeding with more invasive methods, allowing parents to make a well-informed and conscious decision with the support of specialized medical professionals.

The Informed Decision

A morphological ultrasound examination, combined with maternal age, can detect approximately 75% of cases of trisomy 21 during pregnancy. This percentage can, however, increase to 90 to 97% when performed in conjunction with a biochemical test (First-Trimester Combined Screening).

When performed at ultrasound centers and laboratories certified by the Fetal Medicine Foundation (FMF), such as the Germano de Sousa Laboratory Medicine Center, this test ensures the accuracy and reliability of the results.

For their own safety, pregnant women should ask to see proof of this certification. They should also refuse unreliable tests performed using blood drops absorbed onto filter paper.

Do you have more questions about prenatal screening? Visit our page “Questions and Answers About Prenatal Screening” to get all your questions answered.