Attack is not a biological term, therefore it has no scientific meaning. The meaning of "attack" is an aggressive action against a person or place. Unwanted pregnancy qualifies.
Furthermore, it is not wholy the woman's body doing what it does. It is a process that can't begin without an outside force (sperm) acting inside her body, with or without her consent. If it is without, then not only is an attack, but it's an attack coming from an outside source.
If a pregnancy is wanted, then despite whatever damage it may do, it is not an action "against" anything, therefore it is not an attack. Attacks are inherently unwanted.
It is a term the meaning of which hinges entirely on the opinion of the person it is happening to. How the person feels about it determines whether it is an attack. I don't make that decision for any woman; they make it for themselves. And plenty of women with unwanted pregnancies might describe it as an attack. Do some looking around for abortion stories, and you will see them use such language.