Yes, it’s usually a desperate move, usually the baby just gets shelved (Murphy Brown) or aged suddenly (Family Ties), but it never works…
The only one I can think that didn’t harm the show itself was I Love Lucy.
“Bewitched” might be another one… I think that one might have been unnaturally aged though. That one didn’t harm it.
Battlestar Galactica 
Angel.
Although I suspect there may have been a bit of unnatural aging there, too.
[hanging curve ball]
There were a couple of babies born on Voyager and they didn’t ruin the show.
[/hanging curve ball]
Do telenovelas count? Quite a few babies in those, but if the plan was to run for 50 weeks… then for 50 weeks they run, by Jove!
The Flintstones. When it started, both the Flintstones and the Rubbles were childless (kinda like The Honeymooners. Hmmmm…), but Pebbles came on boasrd aftwer a couple of years, and Bamm-Bamm a couple of years later, and the Fluintstones kept on going. Definitely not a hindrance.
Does Glenn Scarpelli count as a baby?
Easily the worst Star Trek TV show ever. Even Shatner’s “Star Trek V” had the memorably bad “Row Your Boat” campfire song. Too bad the Borg never assimiolated Janeway…that would have fried their transistors right there.
I don’t think the baby made a negative impact on Malcolm in the Middle (although you could argue that the show was on the way downhill already at that point). Still, there were some pretty funny baby-related eps, I thought.
Lost, Friends, and maybe Mork and Mindy.
Gotta disagree with this. Much as I love Jonathan Winters, he was shoehorned into a deck chair on the “Titanic” as Merth.
I’m going to have to disagree that Lost counts for this purpose, because the character was pregnant from the beginning of the series, so the baby wasn’t really a new addition.
Well, it the baby itself did provide for the great Wesley storyline, but the baby was also the reason we got teenager Conner, who was the biggest crap-fest of a character to ever be in the Buffy-verse.
“Look at me, I’m so angsty. Oh my God, I hate my dad and I’m angsty. I’m angsty about being angsty.”
Just about worth it all to see Faith make ‘Junior’ kiss the chain-link, though.
“Time for a whu’pn…”
Apparently you didn’t watch the finale.
For those who liked “Mad About You” (relatively few Dopers, I suspect), did the couple’s baby ruin that show?
The multiple babies (Ross and Rachel’s, Phoebe’s surrogacy, and Chandler ‘n’ Monica’s) didn’t ruin “Friends,” I’d say.
I loved Mad About You… and yeah, when they had the baby, it pretty well ruined the show for me.
Give the kid a break - he had a rough childhood. “Angsty” is what you get when your dad doesn’t buy you a car; it’s not “I was raised in Hell by an abusive, manipulative psycho who taught me to hate my father, and now I really want to belong, even though I am utterly incapable of trusting anyone.” There’s “angsty”, and then there’s “fucked up”.
Plus, he had a fun character arc, from Angry Connor to Confused Connor to Delusional Connor to Totally Batshit Insane Connor to, finally, Normal, Well Adjusted Connor.
It’s been awhile, but going from memory, I think it was neither the concept nor Jonathan Winters that ruined the show, but merely that it had run its course by that point.
i.e. “having a baby didn’t ruin it” (as per the thread title), but maybe “a desperate move” that “never works” as per the OP.