Sisterhood of the Travelling Pants movie vs. book

Have you seen the movie and also read the book? I've read the series written by Ann Brashares and I also saw the two movie parts. I'm not quite sure which is better, the book or the movies, but I appreciate the movie better. Anyhow, I've watched the movie first and read the books after, but still I preferred the movie, though I'm a book lover myself. I think something's missing in the book that wasn't in the movie, or it's the other way around. The movie has a part where Carmen (played by America Ferrera) took an acting class and while she was away her mom gave birth to her younger sibling. She had to ask one of her sisterhood friends Tibby to take her place as Carmen's mother's partner. But in the book, Carmen was not taking acting classes while her mother gave birth, she and her new guy friend were out looking for her mother's husband, who was on a business trip. In the movie, also, Tibby who was at that time taking a film making class had to document the delivery of Carmen's mother. Well, it was the director's decision. But somehow, thanks to Brashares and the movie producers for creating that movie and the story.