37 week babies can't shrink can they!? Worried!

[squizita]

Jus had a mw appointment. She has referred me for a growth scan which is fine by me, I know I have a medical condition which can slow growth towards the end.
Bit what is scaring me a lot is... my last scan had me at 36 weeks (it was done 34+4). My last mw appt at 36 weeks - tape measure - had me between 37.
I was seen by 2 mw today and one had me still at 36 ish (OK, I can understand that) but she called a more senior one who measured me THIRTY ONE WEEKS.
Babies can't shrink can they!?! Heartbeat and movement both perfectly OK as is my blood pressure and so on.
I know it's not an exact science but regressing SIX weeks!!!!??

Sorry for typos. Phone.

This happened to me yesterday (suddenly measuring as if I'd shrunk 4cm) but midwife then checked on how engaged the baby was and could only feel 1/5 of her head so said the change was due to her having dropped since last measurement was taken. Have you noticed that your baby has dropped/and or lost amniotic fluid? Hopefully one of those things will be to blame and scan is just a precaution.

Baby has probably engaged and measurements aren't accurate any longer, try not to worry.

Thanks all.
Just re read my notes- they wrote down the less scary measurement. To be fair they were at pains to say the scan would most likely show an awkwardly positioned normal baby BUT if anything was concerning I am past "term" so they'd just induce or c section with relatively low risk.

Trying to re frame this as "wow, in the old days they wouldn't be able to check and sort this out. Aren't we lucky now."
Baby is wriggling away as I type. Doesn't feel little or feeble.