Overly gory, excessively violent films often 9not always0 tend to be of the braindead variety. No plots, no character progression, no emotion, no feeling, just straight into the gore for gores sake. torture porn as alot of it gets labelled. Hostel is a good example. It bored the tits off me because the gore was the focus of the film. the film itself is the excuse for the gory shenanigans. The first Saw film however had a clever plot, great acting, awesome twists and turns. any gore was a part of the story and not the main focus. that kind of switched as the sequels went on but its a good example of the difference.
Unfortunately i think AVPR is of the hostel variety, as in, lets put as much gore in as possible and then think of an excuse to put it there. The predalien and pregnant women thing proves there was no thought into it because it disregards everything the previous 5 films had shown us about the alien. They wanted a gory, shocking scene, and then thought up a shitty excuse to include it.