I'm 29 weeks and measuring small the last two MW checks. Only a couple of cm though, and I think they are a week out on my dates anyway (putting me ahead of what I believe I am) but I'd still prefer not to be sent for a growth scan which is what will happen in two weeks if i'm still not on the 'scale'
BTW I'm very tall, it is my first and I'm having a girl. Also I never put weight on around my belly (legs instead!)if that makes a difference