Is it okay for a 12-week-old fetus to have a light space at the back of the neck of 3.4mm?

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Hello doctor! I am currently 12 weeks pregnant, and the light on the back of my neck is 3.4mm. Doctor let me ask, is it okay for a 12-week-old fetus to have 3.4mm of light on the back of the neck? Can I do a 24 chromosome test now or do I have to do amniocentesis at 17 weeks to be accurate? Looking forward to your advice, thank you doctor!
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Answer Hello, doctor would like to answer the question: "The 12-week-old fetus has a 3.4mm nape of the neck, does 24 chromosomes test or amniocentesis at 17 weeks is accurate? The nuchal translucency or nuchal translucency is an indicator used to assess the risk of the fetus having Down syndrome and other birth defects. Nuchal translucency measurements can provide an accurate diagnosis of about 75% of the child's risk of Down syndrome. There are still cases (small probability), children are at high risk of birth defects but are born completely normal, on the contrary, some children have nuchal translucency measurement results within safe threshold but still can deformities after birth.
Usually the result is less than 3mm, mothers should not be too worried because the risk of Down syndrome is low. If the nuchal translucency measurement results from 3.5mm - 4.4mm, there may be a chromosomal abnormality about 21.1%. If the nuchal translucency measurement result is > 6.5mm, the chromosomal abnormality rate is up to 64.5%. However, nuchal translucency is not the only method to detect abnormalities in the fetus, so to diagnose it, you need to do other tests such as Double test or Triple test or at this gestational age you can do more tests. NIPT test (testing through drawing blood of the mother and performing abnormal screening of fetal chromosomes based on the free fetal DNA present in the mother's blood) to identify a fetus with the syndrome Down or not with accurate results up to 99%. This method is absolutely safe, and easy to do. As for the definitive diagnosis, you can have a biopsy of the placenta or amniocentesis at 16 weeks. However, these are invasive tests and have certain risks. If you still have questions about the thickness of the baby's nape, you can go to a hospital under Vinmec Health System for examination and advice. . Thank you for trusting and sending questions to Vinmec. Wishing you lots of health. Best regards!

Answered by Resident Doctor, Master Nguyen Thi Tam - Clinician - Reproductive Support Center, Vinmec Times City International Hospital