Thanks Xan and Campn - I'm not concerned about it, I think it's just like last time and it's from a simple fluid filled cyst that's burst recently and the fluid just hasn't reabsorbed back into the body yet. I haven't been experiencing any pain or anything. The sonographer said she's almost certain it's nothing to worry about, but she's like to rescan me just to see if it's still there on Tuesday, and if needs be, the consultant will be there for a second opinion.
She also said that it's not interfering with the baby at all so that's the main thing.
The baby was being very well behaved during the scan when doing the measurements and checking the heart, brain, spine, etc it had its arms up either side of its face like it was peeping out at us, but she could still see clearly that there was no hare lip. Just when it came to photoshoot time, the little rascal decided to flip around and face the other way!