Yes, AMNIOS is a Scrabble word!

Letter values in Scrabble US: A 1, M 3, N 1, I 1, O 1, S 1.

Is it a valid word?

AMNIOS is a valid word in the official Scrabble dictionary (US) and the UK Scrabble Dictionary, but not in Words with Friends (ENABLE).

thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals)
(pregnancy) extraction by centesis of amniotic fluid from a pregnant woman (after the 15th week of pregnancy) to aid in the diagnosis of fetal abnormalities

Also: amniotic sac.