There are two common interpretations of this song, however one of them doesn't really fit all the lyrics.
Some say this song is about a carefree singleton female who wants occasional casual acquaintances for fun, leaving the boy the next day, she doesn't want a relationship in her life so a one night stand suits her needs for occasional passion, in this interpretation "baby" means boyfriend for a night.
The alternative interpretation is that the subject is looking to get pregnant and "baby" means a child.
When I first heard the song, and for a long time I thought the second interpretation was correct, however on more careful reading of the lyrics I have changed my mind:-
She woke up late, a day for catching tan and having fun - this is the life of a carefree singleton who has the option to wake up late and suddenly change plans to go on a lazy tan catch. In the alternative "another baby" would have to mean someone who has already has a child with the responsibility and lifestyle of being a parent.
"She leads a lonely life" also fits the story of a carefree singleton better than someone who already has a child.
"Beware of what is flashing in her eyes" - flashing in your eyes indicates desire, whereas "twinkling in her eyes" would mean broody.
So I've now settled on the first meaning, this is a single, carefree girl out for a one night stand and will then dump the boy in the morning, and she has no particular intention of getting pregnant or history of already having one child.