先别急，一定要羊水穿刺才能确诊。

看一下关于NT合并血检的精确率：(http://www.americanpregnancy.org/prenataltesting/firstscreen.html)

A study published in the New England Journal of Medicine in November 2005 determined that first trimester screening was the most accurate non-invasive screening method available. The combined accuracy rate for the screen to detect the chromosomal abnormalities mentioned above is approximately 85% with a false positive rate of 5%. This means that:

• Approximately 85 out of every 100 babies affected by the abnormalities addressed by the screen will be identified.
• Approximately 5% of all normal pregnancies will receive a positive result or an abnormal level.
• A positive test means that you have a 1/100 to 1/300 chance of experiencing one of the abnormalities.

即使你的检查结果是阳性的，胎儿也只有1%到0.3%的可能性不正常（亚裔可能还要低一些）。所以阳性的结果只是意味着你因该考虑做下一步检查，比如羊水穿刺。