AFP AND down syndrom

Sorry it's in english but I'm abroad. triple test results from 16 week. are 1:5. ultrasound screen on week 13.6 was good. but the fetus was at the size of 14.4. Does fetus size AND days difference influence down syndrom chances? I'll be doing amniocentesis of course. i'm just stressed till I return to do it. AND want to understand results a bit better. thank you very much

I'm 40.6 first pregnancy and please write in english OR i won't be able to read it. Thanks

if AFP in down syndrom is reduced cause embryos are relatively small, AND mien was big to its age (ultrasound was taken at 13.6 week, embryo estimated to be 14.4 week) AND still the result is very low (index 0.77) - what does it mean? again many thanks