Tyne Daly's pregnancy was written into the show. In one episode during that time, Cagney and Lacey are out on the street and happen to notice a guy stealing a TV from an apartment—in broad daylight. At first they're amused at his sheer gall, and they shout jeers at him ("Hey, Mr. Television!"), but he winds up giving them a serious chase and they nearly lose him. That's until a hormonal Lacey rounds a corner and screams at him to stop, terrifying not only the perp but a shocked Cagney as well.
Lacey (as they take the perp into custody): I can't run like I used to, Christine.
Cagney: You're a dangerous woman when your feet hurt, Mary Beth.