Love, Rosie order of scenes analysis

I am analysing the order in which scenes appear in this trailer for Love, Rosie, a romantic comedy.

We start with a scene that's maybe 10-15 into the film and then go back to their childhood which is the beginning of the film. 
The film makes many cuts to scenes from beginning and middle of the film, with some at the end. For example, when we see Rosie and Greg about to sleep with each other, which is near the beginning it then cuts to a scene over an hour into the film when Rosie's friend says "You did what?", which is about a totally different situation. I think this is used so the storyline isn't given away and also to create different feels, e.g. happiness and then intensity in the part where Rosie finds out she is pregnant. More evidence is when Alex asks Rosie if she got into Boston and she says no, in the film this scene in after she finds out she is pregnant but in the trailer it is before. This shows that scenes can be jumbled around but still make sense. 

I will take this into account when making my own trailer as I would like to mix the scenes up so they are not chronological and end up giving the whole story away as trailers should tell audiences about the film but not the whole plot. I also want to analyse this trailer at a later date to fit in with my genre anaylsis as it is a romantic comedy aswell as a teen drama.