What's the difference between early Down screening and mid-term Down screening?

Early Down's screening and mid-term Down's screening fundamental difference lies in the detection time is different, there is another difference, is the detection method also has a certain degree of difference. Early Down's screening is eleven to thirteen weeks, after finishing nt, and then blood test PAPPA and HCG these two items; Mid-term Down's screening is to check three items, HCG, AFP and estriol these three blood test items. In addition, early screening generally has other B-ultrasound tests in addition to fasting blood draws, while mid-term screening generally only fasting blood draws. Try not to eat greasy food the day before Down's screening, pay attention to the selection and pregnancy time corresponding to early screening and mid-term screening, because this way can make the test results more accurate.