###Human: Kindly explain the factors used to calculate the risk of trisomy 21. ###Assistant: Hi. I have gone through the query (attachment removed to protect patient identity). Many factors count for calculating risk. They are age, serum markers, family history, and nuchal translucency. An age-related risk is more after 35 years of age. As you are 38 years old, so the risk is calculated as 1:176. But, individually it cannot define the whole risk as it involves other factors also. Nuchal translucency less than 2.9 mm is considered normal, and you have a range of 1.4 mm, so the factor does not show a risk for an anomaly. Serum markers show a least negligible risk like 1 in 20300. So this factor is also not under threat. You have not mentioned about your family history as it will also play a role in calculating the all over risk. So the combined risk is decidedly less. Have a usual anomaly scan at 20 weeks to check for any anomaly. Around 22 weeks, try to have a cardiac outflow tract.