Does the First Trimester Test detect all pregnancies with Down syndrome?
No. About 8 or 9 out of 10 cases of Down syndrome are detected (classified as screen positive). This means that 1 or 2 out of 10 pregnancies with Down syndrome are missed (classified as screen negative). Why do women with screen negative results occasionally have babies with Down syndrome? It is uncommon for a woman to have a baby with Down syndrome and it is even more uncommon for a woman with a screen negative result, but it does sometimes happen. This is because the screening test cannot completely distinguish affected from unaffected pregnancies. However small the risk is, the test cannot completely rule out the possibility of the baby having Down syndrome. Why do you take my age into account? Any woman may have a baby with Down syndrome, but the chance of this happening increases as a woman gets older. Therefore, we use age as one of the factors when assessing your risk of having a pregnancy with Down syndrome. Because older women are more likely to have a Down syndrome baby, they
