Star Trek

Actually, Nana Visitor was pregnant in season four. That's why the producers had to take the baby out of Keiko and put it into Kira. They wanted the O'Briens to have another child and they found out about Nana's pregnancy after they established that Keiko was pregnant.

The producers didn't like the idea that Shakaar was the most logical choice to be the father of Kira's baby and they didn't want to deal with two simultaneous pregnancies on the show.

While the producers were fretting about what to do, Ira Stephen Behr's wife was the one who suggested putting the baby inside of Kira.

If memory serves, Body Parts was the episode where we learn that Kira is carrying the O'Brien's baby. That was close to the fourth season finale and Yoshi was born during season five in The Begotten.

By the way, Nana Visitor had already delivered her son by the time that Kira was about to give birth. She wore a pregnancy pad for the rest of that storyline.

well it was end of 4 some of 5 then.
My bad, I didn't recall where the episode came in the episode lists and automatically assumed that because she was (probably-noticably) pregnant after season 4 finished filming that they did it for like  episode 2 of season 5 (which I now know is incorrect.)

Here's a list of episodes from the official site, you maight find handy.
http://www.startrek.com/startrek/view/series/DS9/episodes/index.html
And her name is not Nina, it's Nana.

I use Memory Alpha, it's fairly comprehensive.

[edit]*whisper* not to mention easier at times, with links so no article hunting*

I learn alot today about Nina and Alex I hope they remain friends for the sack of theire son