Apparently, someone high up thought the Alien's lifecycle was not an obvious enough perversion of human pregnancy.
It's not so much the use of a pregnant woman as Alien fodder; every mistake was in execution. From the egg-barfing to the Predalien's own design, man-in-a-suit vibe and silly behaviour, that scene reeked of artificial horror.
You could make that scene hold so much more impact, although at that stage of production I guess it was already too late.
A redesigned, lithe, creepy Predalien hangs over the pregnant woman, observing her. The lights are flickering on and off as emergency power fails, but the Alien is clever enough to have chosen an especially enshrouded corner to lurk in, its long tail imitating hospital equipment in the shadows. But the woman caught a glimpse. She knows something's in the room with her. And she's in labour.
Her screaming and weeping carries down the desolate, abandoned hallways like the echo of a ghost until, finally, her child is born. The lights flicker and lightning strikes outside, and the Alien looms above her, holding her child. Curious. An experimental application of finger pressure crushes the child, blood and innards escaping from its ruined corpse wherever they can. The Alien, appearing a little disappointed if anything, moves back into its dark place and begins observing the woman again.
