Okay so this has been bugging me a lot. Cersei reveals that she's pregnant at the end of season 7. Since there was no modern pregnancy tests and she still seemed certain of it, she must have been at least a couple weeks into it.
After that these things have happened:
- Jon and company go beyond the wall on a wight-hunt
- They then travel to Kings Landing to show it off
- After that they travel back up north to prepare for the war with the Night King
- They fight the night King
- They travel south once again, this time with a whole army, to fight Cersei
With the fact in mind that travelling from, say, Winterfell to King's Landing in previous seasons seemed like a great effort that took a long time.
Shouldn't her pregnancy at least show a bit after three of these journeys plus a war and one round trip Winterfell - Beyond the wall?
Okay so I've done some calculating on this and this is what I've come up with.
The distance between Winterfell and King's Landing is about 1500miles according to this source
Looking at this map, the distance between Winterfell and the wall is roughly a third compared to the distance to King's Landing, so that makes it 500miles. A horse or cavalry can travel between 30 and 60 miles a day according to this answer on quora
That makes the route from Winterfell to King's Landing at least 30 days by horse under good conditions (counting 50 miles a day here). And in that case the trip to the wall would be 10 days. The average walking pace is about 5km/h or 3.1mph. Walking in this pace everyday for 10 hours straight, would move the army 1500miles in 48 day's. I doubt you'll go faster than that in full armor.
I'll re-use the list from above and add the travel times based o this:
- Jon and company go beyond the wall on a wight-hunt - 10 days
- They then travel to Kings Landing to show it off - 10+30 days - The plus 10 is because they are travelling from the wall to King's Landing and not from Winterfell
- After that they travel back up north to prepare for the war with the Night King - 30 days
- They fight the night King - 2 days
- They travel south once again, this time with a whole army, to fight Cersei - 48 days
This totals to 130 days. On top of that we have to count in a couple of week's beacuse Cersei could'nt know from day one that she was pregnant. Let's say 20 days and we're up to 150 days or ~5 months.