Thanks fionajill, sarah_h and csab.

my last scan was at 19 weeks and all was fine measurement-wise.

i know the ultrasound measurements aren't terribly accurate - the sonographer told me the accuracy range but i can't remember what it was - but she seemed to get a very clear head measurement. my ob had given me a size estimate of something like 3.2 - 3.6kg and my uterus has been measuring normally, although i know these things are quite variable.

now i'm wondering, if the baby's so small, what the hell's in my uterus that's making it so huge??!