Prometheus 
"net word count now reduced so that can't be used as an excuse for deleting constructive contributions"

 It was not an excuse, it is an unnecessary detail. Unless you have some ulterior motive for him doing it, he does it because they don't have the equipment or staff to deal with a pregnancy especially an alien one. The only important part is she finds out it is inside her, she gets it removed. Don't be bitchy in edit summaries, it's tedious.

Given Weyland's instructions to infect somebody (whether David picked Holloway because he patronised him, or whether Weyland picked him, is unclear) at the cost of their own life to get hold of Engineer genetics, "an ulterior motive" - that they are more interested in the alien than in her, and that they don't share her Ripley-ish instincts that the alien just needs to be killed - is a pretty clear inference. Or alternatively she might just be worried that Vickers will kill her with a flamethrower when she finds out Shaw is also "infected". Either way, I suspect other people may feel the same - and indeed it's the sort of plot point which somebody whose attention has drifted or who has nipped out for a pee could miss at first viewing. Being a barnstarred editor of film articles does not mean that your humble opinion of which plot point is important is correct and everybody else's isn't, although I'm glad to see that it's been left in. And please don't leave bitchy messages on the talk pages of constructive contributors - to coin a phrase, it's tedious.