Chromosomal abnormalities involve changes in the number or structure of chromosomes, exemplified by conditions such as Down syndrome, Patau syndrome, Edwards syndrome, DiGeorge syndrome, Turner syndrome, and Klinefelter syndrome. These changes can arise from various factors, including errors during cell division, parental inheritance, or environmental influences like radiation, toxic chemicals, and certain medications used during pregnancy. Such abnormalities often lead to birth defects or severe medical conditions that impact physical development.

While ultrasound cannot directly visualize chromosomes or provide a definitive diagnosis, it serves as a crucial initial screening and risk stratification tool. This technique assesses fetal morphology, screens for structural anomalies, and monitors fetal development. When structural defects or genetic abnormalities are detected, ultrasound guides subsequent management steps, such as non-invasive prenatal testing (NIPT) or definitive invasive diagnostic methods like amniocentesis or chorionic villus sampling.

During the first trimester of pregnancy (11-13 weeks), doctors use ultrasound to assess key biological indicators for estimating the risk of chromosomal abnormalities. These signs include nuchal translucency (NT), nasal bone index, blood flow through the tricuspid valve, and the ductus venosus. Increased nuchal translucency or hypoplastic nasal bone can indicate a risk of the fetus having Down syndrome, Patau syndrome, Edwards syndrome, or congenital heart defects. When ultrasound information is combined with maternal age and biochemical blood tests, 90% of Down syndrome cases can be detected with a false-positive rate of approximately 5%.

In the second trimester of pregnancy, ultrasound screens for structural defects in the nervous, cardiac, digestive, and urinary systems. The simultaneous appearance of multiple abnormalities or major defects significantly increases the likelihood of chromosomal abnormalities.

Dr. Nguyen Hoang Long performs an ultrasound for a pregnant woman. Illustration: Tam Anh General Clinic District 7

A normal ultrasound result does not completely rule out genetic risks, as many fetuses with chromosomal abnormalities, such as Down syndrome, may not show visible signs on ultrasound images.

You are 7 weeks pregnant; at this stage, ultrasound primarily helps determine the pregnancy's location, number of fetuses, fetal heartbeat, and embryo size, while also assessing the uterus and adnexa. The risk assessment for chromosomal abnormalities will be performed in the first trimester (11-13 weeks 6 days). Given your family history of chromosomal abnormalities, you should visit a specialized Fetal Medicine unit. A doctor there can thoroughly understand your specific condition and family history to determine the appropriate tests and timing. You also need regular examinations and ultrasounds to comprehensively monitor fetal development and maternal health for safe pregnancy management.

Dr. Nguyen Hoang Long

Fetal Medicine Unit

Tam Anh General Clinic District 7