I had my first sono at 5w 5D (or what I thought was)

And I went back today (2 weeks after the first) and did they another to check for heartbeat. They found a heartbeat but they measured the baby at 6 w 4 d.

My question is, are early measurements not as accurate? They found a heartbeat so baby is growing, I’m assuming.

But I should’ve been measuring 7+weeks today.

Is there a chance baby may not be growing fast enough, or just measurements not as accurate this early on?

Thanks!!