How Pregnant Am I?

7 weeks, 3 days: Went in for my third sonogram this morning, and I had a different doctor, an OB/GYN, as my regular RE was on vacation. We did the sonogram, everything was fine. Heartbeat was there, we got the close-up of the fetus, she printed me out a copy of it in all of its Sea Monkey-like glory. Then I asked how far along I was. "6 weeks, 5 days," she replied. Huh? How can there be a difference of 5 days? We know when my last period was, we know when I was inseminated. Does that mean G had supersperm that packed emergency rations and lived in the uterus for at least five days, vs. the supposed 72 hours?

When I asked the RE how she could explain the difference, she said it was all by how long the fetus was. Which seems like a really, really inexact way to gauge anything, considering the fetus is about an inch long and curled up. So we can make a woman ovulate multiple eggs, remove them, freeze them, defrost them when needed, inseminate them, and replant them in her uterus, where they have a chance at developing into a living being, but we can't figure out how old a fetus that's hanging out in the womb is?