Wrong gestational age used to figure probability for Down Syndrome


Q: Good day. Is it possible to get a false or wrong test result for Down Syndrome if the gestational age was entered wrong? I was 16 weeks at the time of the blood test and they entered the age as 20 weeks. They first told me that there was a high probability the baby will have DS, then called back and informed me of the mistake and just told me that I would have to wait for the new results, without giving anymore info. Of course we will love the baby just the same, but this is a bad experience for a first time mother (refering to human error, that is) Thank you for your time!


A:   The main usefulness of ultrasound is to confirm the gestational age of the fetus. Another benefit of the ultrasound can also pick up problems of a serious medical nature, such as blockage of the small intestine or heart defects. Some studies have showed that there was a strong association between the size of a collection of fluid at the fetal neck, called nuchal transluceny, and the risk of Down syndrome, making an ultrasound measurement useful as part of the first trimester screen. It is important to keep in mind that even the best combination of ultrasound findings and other variables is only predictive and not diagnostic. For true diagnosis, the chromosomes of the fetus must be examined. Since there was a error during ultrasound, a maternal serum screening can be done at 15 to 20 weeks of pregnancy to screen for Down syndrome and Trisomy 18 if you have not had a first trimester screening or integrated prenatal screening.

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