Hi, ultrasound in pregnancy 1st; 6 to 7 wks for cardiac activity, 11wks level one for down syndrome screening, 3rd: 19 wks level 2 to see each and every organs.28 wks and 36wks doppler study these r minimum. If any growth retardation, bloodpressure and
sugar in pregnancy it should be done frequently.
Ultrasound is a sound wave so no harm to do even in each week......