My weight has really jumped as well, though I only seem to be weighed before scans as well - but it was up by 2kgs between nuchal and anomaly, but then another 6kgs between anomaly and placenta site scan.
Though that was right after a week's holiday during which I treated myself to ALL the milkshakes...
And it does seem like everywhere does it differently with the fundal height measurements - I was measured at the 25-week check (though I was 25+6), and again a couple of days ago. And both midwives (I've yet to see the same person twice for anything during this pregnancy - I'm starting to think I probably won't at all) have seemed to take it fairly seriously, though I don't know what they would have done if I hadn't measured exactly what they thought I should for my dates...
We've also decided to go for a postnatal doula, and I feel so happy with that decision. We haven't got much of a support network where we are, so it's just really nice to know that there will be someone around to help us out in figuring out how to care for a baby in the first few weeks - and she'll be a familiar face, for once! Plus, she's also a birth doula, so she gave me a few pointers for what it might be useful to put in my birth plan (ie, as few people in the room as possible, always explain examinations before doing them, the BRAIN acronym) - instead of the wishful thinking I was wondering if I was meant to put (eg, go to hospital, have baby 30 minutes later, go home 3 hours after that). 