Continuity mistake: When Doug goes to meet up with Ray, Richie zips up his jacket. In the next shot his jacket is unzipped. (00:06:20)
Train Wreck - S1-E20
Continuity mistake: When Julie goes to get her jacket, Doug's board swaps hands instantly. (00:03:40)
Train Wreck - S1-E20
Continuity mistake: When Ritchie is pretending to be Carrie, Doug has hold of his cue with both hands. Camera cuts and he's not holding the tip any more. (00:06:05)
Train Wreck - S1-E20
Continuity mistake: When Doug sees Arthur's headstone in the yard, the dark opaque flap of the dog door is missing from its frame, but it reappears as Doug enters the kitchen. (00:06:40)
Train Wreck - S1-E20
Visible crew/equipment: At IPS, while Doug gives his speech about using heavy package stickers, in the shots facing the drivers seated at the table, the end of the IPS set and a crew member are visible at the right side of the screen. (00:08:45)
Train Wreck - S1-E20
Continuity mistake: When Carrie turns up at IPS, she holds out the coloured char with two hands then one depending on the shot. (00:09:50)
Train Wreck - S1-E20
Visible crew/equipment: When Arthur asks Doug for help with the epitaph, the green and red tape markers are visible on the floor in front of the dishwasher, where Doug stands. (00:12:00)
Train Wreck - S1-E20
Continuity mistake: When Arthur is rewriting his epitaph, the pad and pencil keep moving between shots. (00:12:10)
Train Wreck - S1-E20
Visible crew/equipment: When Carrie grabs the mail off the floor if you look in the window behind her you can see the pole of a boom mic moving around. (00:12:45)
Train Wreck - S1-E20
Revealing mistake: Shari from ISP radios Doug about the rush order pickup at 1202 Stratford, so Doug pulls over and soon Carrie pulls him to the back of the truck. Cut to exterior shot of the truck, and the street sign reads "Lafayette, Culver City" which reveals the California location. The truck is parked on Culver Blvd, corner of Lafayette, in front of the well known Washington Building (awnings are now black), which is located a few blocks up from Sony Pictures Studios where King of Queens was filmed. (00:21:35)
Hungry Man - S1-E21
Continuity mistake: At the start Arthur goes from cutting bananas to having his hands on the side in between instant cuts. (00:01:10)
Hungry Man - S1-E21
Revealing mistake: When Arthur plugs the blender in you can see the wall move. (00:02:25)
Hungry Man - S1-E21
Visible crew/equipment: When Doug explains he's working the double shift a white tape marker is visible on the floor by the front door. (00:03:20)
Hungry Man - S1-E21
Revealing mistake: When Deacon drops the suit off to Doug, Doug parks the truck up and Deacon gets in, however the outside of the truck is still moving as if Doug is driving. (00:07:50)
Hungry Man - S1-E21
Visible crew/equipment: When Spence is pacing there are tape markers visible on the floor where he turns. (00:17:20)
Hungry Man - S1-E21
Visible crew/equipment: When Arthur accuses Spence of trying to push him out, there is a white taper marker visible on the rug where Arthur stands to accuse him. (00:17:50)
Answer: To answer the question directly. Carrie and Doug do not have a biological child during the show's main run. In season 3 or 4 finale (cant remember which) Carrie has a miscarriage. Later on in the show they find out Carrie has 1 working ovary. Thus reducing the chance of them conceiving. By the final season, they couple agree to adopt from China and go to collect their child in the show's final episode. While on the flight back from China it's revealed that Carrie is once again pregnant. However the last scene of the show is a flash forward showing that Carrie goes full term with that child and they are struggling with both kids.
Ssiscool ★
Adding on to this answer, I read somewhere that producers were afraid of the show having a "before baby" feeling and then an "after baby" feeling. Some fans feel that main characters, or the show in general, decline in quality after a major change. For example, Jesse and Rebecca on "Full House" after they had twin sons, and Daphne on "Frasier" after she married Niles.