OK, so you'll have to excuse my idiocy.

What EXACTLY are the brim measurements? Last week the baby was 5 fifths above the brim, now he is 4 fifths.

Is the brim the cervix and the birth canal measured in fifths?

I know the baby is very low as he is now pressing on my right pelvic bone quite hard and has only been doing so the last couple of days. So, I reckon he's dropped significantly.

My other question is, am I correct in thinking that the optimal birth position for the baby is with their back against one of your sides? I've heard if the baby's spine is aligned with yours, you are going to have back pain during birth.

Jellybean's back is against my right side - very convincingly.