Measurements Approx:

Length: 51"
PTP: 23"
Sleeve: 18"

Medium 
ILGWU Union Tag
Style 38815
70% Nylon
30% Polyester 
Made in USA 

This is a true vintage rare piece. 
Has some pulling in multiple areas- see photos, some examples on sleeves and on back that I could see. Color is a beige/ivory.

1970s Vintage Christian Dior Nightgown Maxi Union Medium Lace Embroidered Ivory