2 blighted ovums since august then diagnosed with subclinical hypothyroidism. lh surge 4/24 -hpt 5/4 +hpt 5/5. 6.3 week scan showed yolk sac. 7.3 week scan showed baby measuring 5 week 6 days with heartbeat but not measurable. should i be concerned?

Even with an "LH surge" on "4/24", actual fertilization may have occured between 4/26-29 with implantation on 4/30, which may account for the discrepancy between the 7.3 w scan and the 6.3w scan. An U/S showing a size of 5w6d may also represent the technician's margin of error. Viable fetal heart is an optimistic sign, as measurements are subject to human error.