There was an interesting article on fetal pain in the New York Times magazine. I’m not an expert, but I thought it gave a pretty good overview of current scientific/medical viewpoints based on things I had previously read (a previous lengthier post on this topic is here).
My opinion is that given the trend in research findings here (and in related areas like awareness in brain-damaged patients and animals) it is increasingly untenable to keep to a view that only fully developed healthy human nervous systems “count” when assessing whether meaningful first-person experience exists. The pain experience felt by a 20-week old fetus that lacks a developed cerebral cortex will almost certainly differ from ours, perhaps to the point that it shouldn’t be called “pain” at all. But to assume that the stress responses observed are not accompanied by some meaningful correlated experience seems highly dubious. Given the limit on our ability to know “what it’s like” in the absence of a first-person report, it makes sense to err on the side of caution.
UPDATE (25 Feb.2008): please see also the post on this at Conscious Entities.