Bristo Palin Pregnancy Photos - Current Pregnancy
On September 1, 2008 the McCain campaign announced the Bristol Palin was currently "five months" pregnant. They did this in a direct attempt to sidetrack rumors that Trig was Bristol's child and that Sarah was his grandmother. At the time the McCain campaign stated that she was "about five months" pregnant. Here is the official Palin family statement.
We have been blessed with five wonderful children who we love with all our heart and mean everything to us. Our beautiful daughter Bristol came to us with news that as parents we knew would make her grow up faster than we had ever planned. We're proud of Bristol's decision to have her baby and even prouder to become grandparents. As Bristol faces the responsibilities of adulthood, she knows she has our unconditional love and support.
Bristol and the young man she will marry are going to realize very quickly the difficulties of raising a child, which is why they will have the love and support of our entire family. We ask the media to respect our daughter and Levi's privacy as has always been the tradition of children of candidates.
The announcement immediately was greeted by a range of response, from complete acceptance of the word of the campaign, to total skepticism, based in large part on the very convenient timing - a "five months" pregnancy was required to preclude Bristol's having given birth to Trig, and a five months pregnancy was what they got.
Then, in mid October, Levi Johnson, the young man who had been identified as the unborn child's father announced that Bristol Palin's due date was December 18th. This gave a very concrete timetable for the alleged pregnancy.
Given a due date of December 18th, here's a chart that shows weeks of pregnancy.
Here's the photographic evidence that exists from Bristol Palin's current reported pregnancy.
July 10, 2008 - (approx.) At the Philadelphia Zoo. Seventeen weeks
July 17, 2008 - At the Governor's Picnic in Wasilla Eighteen Weeks
Here's a picture of Bristol and (probably) Trig from the same event.
Augsut 22, 2008 - approx. Alaska State Fair Twenty three weeks
September 1, 2008 - Twenty four weeks (5 1/2 months)

September 3, 2008
September 4, 2008 - Twenty five weeks
October 18, 2008 - Thirty one weeks
November 4, 2008 - Thirty three weeks
Bristol Palin Pregnancy Photos - Trig Palin
A lot has been made of two separate photos in which Bristol appears to have a "baby bump."
Update: 9/24/08 BOTH of these photos have been disproved as showing any pregnancy. I am leaving them posted here because I want it to be clearly documented that neither of these photos show Bristol Palin pregnant. This is important, because some of the websites that were attempting to give information about this issue became bogged down in debates about these pictures, and the fact that the date was discredited was viewed as proof that Bristol Palin could NOT have been pregnant in April of 2008. So here's the bottom line. Neither one of these pictures was taken at a time where ANY conclusion can be drawn about whether or not Bristol Palin was pregant in April of 2008. But she could not be visibly pregnant in either of these pictures.

The first photo was definitely published in the Anchorage Daily News on March 9, 2008 though when it was taken is unclear. (Update: It was taken NO LATER THAN 10/23/07) Some "pro-Palin" people have indicated that this picture was taken in 2006, in order to disprove any chance that Bristol is pregnant here. The view through the windows shows NO leaves on the tree. Neither Sarah nor Bristol look terribly pregnant in this photo, though it's easy to see why some people have suggested that Bristol has a baby bulge here. Without an accurate date no conclusions can be drawn. (Update: She could not have been visibly pregnant in this photo.)
(Update: Based on additional evidence, I think it is LIKELY that this picture was taken in fall 2006.)

Update (9/24/08) "Baby Bump" disproved. This photo, which was taken by Anchorage Daily News Photographer Mark Lester appeared in the Anchorage Daily News on October 23, 2007. It is identified as being taken at the Palin's home at Lake Lucile in Wasilla. There's no confirmation that the photo was taken that day (i.e, October 23). It could have been taken months earlier. But the family is clearly wearing the same clothing as in the larger photo above. (We can't see Bristol's shirt, but Sarah's jacket, Piper's shirt, and Willow's shirt are all the same.) Given a due date of 5/15/08, IF this picture was taken on 10/23, no matter who is or is not pregnant, it would not have been beyond 10-11 weeks, way too early to show, particularly on a first time mother. (Update: Additional evidence makes it likely that this picture -and the one above - were taken in the fall/early winter of 2006)

I cannot find any reliable source that states when this picture was taken. Numerous places state that it was taken in February of 2008. The green leaves clearly visible on trees seem to bring that statement seriously into question. I cannot imagine anywhere in Alaska that would look like this in Febraruy. In my opinion, Bristol Palin does not look pregnant here. Neither does her mother. If anyone can identify unequivocally who took this picture, where, and when it would be very helpful.
Update: A reliable correspondent has identified this picture as being taken in Juneau in late summer or very early fall. Across the water in the background is Douglass Island. No snow is visible on the mountain at all, and according to my source, some snow is visible typically by early fall. What summer is unclear, I guess it could be either 2007 or 2006, but whenever the photo was taken it was too early to have any relevance to this issue.