Womb Chair and Ottoman  

probably
If the chair has a Knoll label it is authentic. The ottoman probably is as well if they are matched. A photo of the frame, label, and overall chair will help determine age.

Womb Chair and Ottoman
just found out from Knoll that because the label is with a Madison Avenue address in New York, that this chair is authentic and it is their most prestigious of showrooms they had ONLY in the 70's

A label doesn't guarantee authenticity...
Search Ebay for "herman miller tag"; there are four metal tags up for sale at the moment, at prices from $25 to $35. Knoll paper labels are even cheaper.
The Womb hasn't been widely copied, though, so your chair probably IS authentic. If you have any photos of the chair -- showing the metal frame viewed from below, the seat with and without its cushions, and maybe the stitching and the glides -- it'd be nice to see them.

Don't forget the cushion retention straps
Mine is original,and has them on the seat bottom.

Yeah, that's...
Yeah, that's one of the reasons for the photo of the seat without its cushions.

womb chair
i am not sure if the pictures will be posted. please let me know

womb chair seat straps
does that look original to you?. I posted a picture

womb chair
there are some pictures of the stiching, legs and glides. what do you think> does it look authentic? do you have an authentic one?

Looks authentic to me.
I'm no expert... But as far as I can tell from the photos, your chair looks like my Knoll chair and does not look like the reproduction that a number of people are selling on Ebay.