Interestingly, Dr. Pulaski never actually wore the standard TNG jumpsuit during the show itself, but she did wear that uniform in at least one publicity photo for The Next Generation’s second season. (See right.)
While I haven’t been able to verify this, according to Memory Alpha, “Diana Muldaur stated that the original one-piece uniform was very uncomfortable and that she had felt the tight uniform was not flattering for a middle-aged woman.”
Considering how vocal most of The Next Generation’s cast has been over the years about how much they hated wearing the skin-tight TNG jumpsuits for those long filming days, I think safe to assume that there’s probably some truth behind the sentiment.
I suspect that actress Diana Muldaur, costume designer Durinda Rice Wood, and/or “The Powers That Be” weren’t thrilled at the prospect of dressing the character in the only other uniform option William Ware Theiss had established, the TNG skant.
Thus, a new costume was needed for the character.
And there was certainly precedent for the ship’s Chief Medical Officer (and medical personnel in general) to have their own unique uniform.
In The Original Series, Dr. McCoy often wore a medical uniform variant (as did Dr. M’Benga), which was analogous to the standard TOS uniforms but still unique.
Nurse Chapel also had her own unique variation of the “starburst dress.”
In the TOS movies, costume designer Robert Fletcher had given medical personnel a uniform option that was less of a “variant,” and more of a “class.”
And during The Next Generation‘s first season, Dr. Crusher often wore a lab coat, which helped establish a unique look for her character.
On the subject of uniform classes, variants, precedent, and evolution, you may also be interested in this blog post and its corresponding video:
And of more direct relevance, see this post (and its corresponding video) on the topic of the TNG-era uniform paradigm – why I believe TNG’s uniforms were conceived and designed the way they were:
In any event, rather than simply continuing with the established “lab coat” option, costume designer Durinda Rice Wood chose expand Theiss’ uniform family and dress Dr. Pulaski in a medical smock more analogous to Dr. McCoy’s from The Original Series – which seems appropriate somehow, considering the similarities between the two characters.
Although the TNG medical smock was unique, it obviously belonged to the early TNG-era uniform family and shared several major characteristics with its TNG jumpsuit counterpart, and indirect predecessor, the TNG skant.