I had an ultrasound at what my lmp would've made 7 weeks and 2 days, but I have longer cycles (an average of 33, but 30 was the shortest it had been in over 6 months, and that was the cycle right before I got pregnant.) The scan put me at 6 weeks and 3 days. To my understanding, even early ultrasounds can be off by 5 days, and it gets even more sketchy as you get further along? I didn't have another opportunity to have a scan until 13 weeks 1 day, and that put me at 13 weeks 3 days. Then my scan at 15 weeks 5 days put me at 15 weeks 6 days. I'm trying to figure out when I ovulated. After reviewing the first scan and my blood work, my doctor put me at 6 weeks 4 days. With that being said, the first scan put me ovulating on Oct. 18, doctor put me at Oct. 17, second scan put me at Oct. 15, and the third scan at almost 16 weeks put me ovulating on Oct. 16. Is it safe to say I ovulated somewhere between the 15-18. I'm trying to rule out ovulating on the 13th. My lmp was Sept. 28.