W/my first child i had a sonogram at 8,12,16,20wks. w/current pregnancy she said the 1st would be 20wks. why the difference? can i request more?

Hard to say: The timing and frequency of sonograms is usually driven by need.Some information obtained during the initial evaluation may suggest the need for more monitoring than others. Your first pregnancy likely triggered some concerns that are not present now.More exams would not hurt baby, but may not be paid for by insurers unless they meet the "need" requirement.