By last period i would be almost 8 weeks. Last week I had a follow-up ultrasound Thursday and showed baby measuring 1 week behind, no concerns as heartbeat is strong and I tend to have little babies. I am wondering when you would.test for sneak peak. We did one early last week and it came back unconclusive Wednesday but I'm wondering now if thats because I'm measuring behind from LMP. I want to do this and get as accurate results as I can since this is pregnancy#6 and we have 3 girls at home now.