Caroline is holding high teas for her friends and she wants them to be insanely jealous of the food. Gabi and Caroline get into a conversation about cup sizes rather than cup cakes which gets Gabi to think she might be pregnant after her encounter with Josh.
As she desperately tries to have a pregnancy test it only sets off a chain of gossip where Eliot and Yolanda think that Caroline has become pregnant and she is going to announce it at the party. Caroline does have a surprise for Josh but it is a prize horse that her father won at an auction.
I think the writers have done well to stretch out such this material, they obviously contrast Gabi's personality; young and tarty with Caroline's; young, rich and aloof.
Four episodes in and you think they would had reached the limits of that one night stand apart from Caroline finding out about it.