Hi mei, don't worry! The tests are usually ordered by doctors after examining us. If doctor suspect complications, then will order more tests. Sometimes, extra tests are done cos we request for them for reassurance also. The important scans are only the dating scan at 6 to 8 weeks and the detailed scan at 19 to 22 weeks. If you are older than 30, or above 35, you may be offered extra tests, esp if the dating scan shows that the fetus may be abnormal. If you are under 30, in good health, no previous miscarriages, or still births, then you are likely to only go for 2 scans in your entire pregnancy. However, if you dun know your blood group, or if you are not sure if you are immune to diseases like chicken pox, rubella, hep B, you may have your blood taken to check. If you have complications like severe cramping or spotting, you may have blood taken to check for HCG levels and more scans done.