Four first trimester ultrasounds done at 7 8 10 12 week all come. up with same conception date. what's it mean??

Good estimates: One scan gives a good estimate of the conception date. A second scan that gives the same estimate, just gives more confidence that the first scan's estimate is accurate. Accurate means plus or minus one week - because nobody knows exactly when conception happens. However, if a woman knows exactly when she had sex, that can point to the conception date. Normally, people don't get so many scans.