A 10-week ultrasound serves as an early opportunity in prenatal care to assess a developing pregnancy. This scan helps to confirm the presence of a heartbeat, determine the number of fetuses, and establish gestational age and estimated due date by measuring crown-rump length. It provides reassurance and can identify major fetal anomalies.
Screening for Down Syndrome
The 10-week ultrasound plays a role in screening for Down syndrome through nuchal translucency (NT) measurement. Nuchal translucency is the fluid-filled space at the back of the baby’s neck. A thicker measurement in this area can indicate a higher chance of Down syndrome or other genetic conditions, as babies with genetic disorders often have more fluid.
This NT measurement is combined with maternal blood tests as part of the “first-trimester combined screening.” Blood tests measure levels of specific hormones and proteins, including pregnancy-associated plasma protein-A (PAPP-A) and free beta-human chorionic gonadotropin (hCG). Low levels of PAPP-A and high levels of hCG can suggest an increased possibility of Down syndrome.
Interpreting the Ultrasound Results
The 10-week ultrasound and combined screening are screening tools, not diagnostic tests. These screenings provide a risk assessment for Down syndrome, rather than a definitive diagnosis. An “increased risk” result means there is a higher chance the baby might have Down syndrome, but it does not confirm the condition.
Screening tests can produce false positives, suggesting a risk when the baby does not have the condition. Conversely, false negatives can occur, indicating a low risk even if the baby does have the condition.
Next Steps and Confirmatory Tests
If the 10-week ultrasound or combined screening indicates an increased risk for Down syndrome, further evaluation is recommended. Non-Invasive Prenatal Testing (NIPT), also known as cell-free DNA screening, is often the next step. NIPT analyzes small fragments of the baby’s DNA circulating in the mother’s blood, available from 10 weeks of pregnancy.
NIPT is an accurate screening tool for Down syndrome, with a detection rate of 98-99%. While more accurate than first-trimester combined screening, NIPT remains a screening test and does not provide a definitive diagnosis. A positive NIPT result indicates a high likelihood, requiring confirmatory diagnostic procedures.
Diagnostic tests, such as Chorionic Villus Sampling (CVS) and Amniocentesis, can provide a conclusive diagnosis. CVS involves taking a small sample of cells from the placenta, performed between 10 and 13 weeks of pregnancy. This procedure carries a risk of miscarriage, less than 1%.
Amniocentesis involves collecting a sample of amniotic fluid surrounding the fetus, performed between 15 and 20 weeks of pregnancy. Both CVS and amniocentesis analyze the baby’s chromosomes for definitive confirmation of conditions like Down syndrome. Amniocentesis also carries a risk of miscarriage, less than 1%.