Social mores of the time make this a very curious sequence by modern standards. Perdita is giving birth while Anita and Nanny attend, but they are kept almost completely off-screen. This kind of birth scene dates back at least as far as Stagecoach (1939), where the camera concentrates on those waiting rather than on the woman. That approach is consistent with how I Love Lucy or The Flintstones handled birth, concentrating on the comic aspects of the expectant father rather than on what the mother is going through.
This film is slightly different as Roger revives one of the pups. In effect, female effort is invisible while male effort is highlighted. Female effort is just nature taking its course while male effort requires ingenuity. While I'm sure that Bill Peet did not intend any slight, when I consider this sequence and how poorly developed Anita's character is, I see a subtle devaluing of women.
(I know that Roger's actions are from Dodie Smith's original novel, but in the novel, the Anita character is more present during the birth than she is here. Undoubtedly, Smith's ability to write about birth without making it visually explicit gave her the edge over Peet.)
Anita is almost invisible in this sequence, and where she is present she has weak attitudes and next to nothing to do. She is saddled with exposition and to provide Cruella with someone to talk to. "That's right Cruella. They'll have their spots in a few weeks." "Well I'm sure we'll get along." "Well Cruella, he seems..." Try putting an emotional performance behind lines like that. Why wasn't Anita the one to perform some of Nanny's business? Why wasn't Anita given more backbone to stand up to Cruella? Since this scene severs their relationship, why not have Anita oppose Cruella forcefully instead of letting Roger do all the work? Roger gets to save the puppies twice. What does Anita get to do except admire Roger's actions?
The staging in this sequence is simple but effective. We're practically looking at a stage set with all the action playing in a single plane from left to right. The characters are often isolated by the camera, but there is never any confusion as to where they are relative to the other characters.
There's a bit of odd geography in this sequence. We know that the characters live in a row house, so the kitchen door is not accessible from the street. Yet Cruella comes in through that door, so somehow she got into the yard.
The identification between dogs and owners is continued here, ironically through Cruella's actions. When she can't get her pen to write, she splashes ink all over Roger, making him as spotted as Pongo. It's appropriate that he look so dog-like just before he acts on the puppies' behalf by denying Cruella the chance to buy them.
Ollie Johnston handles Nanny for the most part. In contrast to Anita, she has things to do and is enough of a caricature to give an animator something to work with. Milt Kahl continues excellent work with Roger. Roger waiting tensely for the birth, his celebrating by dancing with Pongo, and his refusal to Cruella are all vivid. Frank Thomas handles the revivial of the puppy including Pongo's reaction shots. Thomas gets Pongo's reaction shots to Cruella and the final conversation between Pongo and Perdita. Thomas always gets the shots with a clear, strong emotional through-line.
Marc Davis continues his bravura performance of Cruella. She dominates the sequence by her aggressiveness. Her disgust at the puppy's lack of spots, her contemptuous laughter at Roger's economic prospects, her annoyance at her pen and her full-out anger when she's refused are all communicated with great exuberance.
Blaine Gibson really knew how to move a dog believably. He never seems to get scenes with real acting in them, but whenever there's a scene of a dog moving from one place to another, it seems to fall to Gibson. Here, he gets the scenes where Pongo barks at the exiting Cruella and when he goes to join Perdy in the basement.
Poor Les Clark was capable of better animation than they've given him to do with Anita here. Anita's standing in this movie and Clark's standing in the animation department are, sadly, analogous.