Don't panic
I'm going through something similar - my guy has had short femurs for two scans now, I'm just waiting for results from the third. I did a lot of research on it. The two most likely scenarios are that your baby just has short legs, or that it's IUGR. Take a look around at your family and dad's family, and see if you can get any clues there. I know my DH and his mother both have short legs, so I'm guessing that's a factor for my baby. It could also just be a matter of measurement error, or different parts of your baby growing at different rates - only future comparison scans can really tell you for sure. Since the rest of your baby is measuring in the "healthy but small" range, it's less drastic a difference than it would be if a big baby had such short femurs - at this point it's really a matter of a couple millimeters.
If it
is IUGR, it's not as scary as it sounds (and trust me, I know how terrifying it sounds). You're being monitored closely, and they'll step it up if they need to. If they see signs that the placenta or cord aren't doing their job, they may decide to deliver you early, but you're already at a good gestation, and it's unlikely to suddenly get desperate tomorrow. Everything I've read said that IUGR babies who are delivered early end up thriving once they're out, once you're past the point that premature birth itself is super risky (and you are past that point).
In the studies I looked at, the actual risk of short femurs meaning anything other than short legs or maybe IUGR are really low - it's extremely unlikely to be anything more serious, despite the scary stuff you may find on the internet.
The one thing that's been stressed to me is to make sure I'm very alert to his movements. I'm supposed to call in if there's any decrease outside of his normal range. He's allowed to have lazy days, so long as they're normal lazy days. Keep on top of that, and call your doctor if you have
any concerns about movement.
