I had my first ultrasound today and am measuring a week behind where I thought I was. Based on my LMP I should be 7w1d and based on when I think I ovulated I should be 7w2d. Baby was measuring 6w1d with a heart rate of 114.

I'm not 100% sure of my ovulation date - I'm just guessing based on CM/past cycles. However, we only BD once that cycle and even if we conceived at O-5 I should be 6w5d... My OB didn't seem to be worried at all but I have a follow up ultrasound in two weeks.

Sorry for the rambling but should I be concerned? Anyone have experience with a similar situation?