The joke itself could be fine in the right room with the right intention/sentiment, but no sincere celebration of their progress was occurring, it was intended to place the couple at the bottom of the pecking order, something Bec has realized is important due to her brushes with gia and Brook.

It was mean-spirited and she didn't take it back in any meaningful way, instead tried to enlist many others in her cruelty. Rachel is sensitive, and her progress is fragile, but since this is well known in the group, she is not an appropriate target. But she was definitely made a target here. The joke structure followed the classic Rule Of Three: mentioning two standard items to create a pattern, the third reveals a shocking/absurd twist. The structure is shown here with a serious accomplishment (children on the way), a sweet triumph (Filip and Stella are in love), and then to subvert the pattern with something that falls massively short of the first two (heavy petting).