Visible crew/equipment: At the end of the episode when Carrie and Doug are arguing about her letting him win a ping pong game, all the windows over the bed are closed, they leave the bedroom to go play a rematch, when they return to the bedroom Carrie starts pushing Doug down on the bed and the middle window is open, as they lay down further you can see someone swing the window shut. (00:27:00 - 00:28:00)
Revealing mistake: In the final scene, Carrie starts to kiss Doug and pushes him onto the bed. The camera angle switches from what would be outside the window to beside the bed. The scene was done in one take from 3 camera angles. As the camera pans left you can see the center window is completely open because they had just pulled the camera out of it and didn't get it closed yet, and you can watch the window be closed by an invisible hand from underneath. (00:28:00)
Continuity mistake: When Arthur asks Doug for a game of ping pong, a ball suddenly appears under his bat and then disappears and Doug throws him the ball to have the first serve.
Continuity mistake: In the scene where Spence is entering the place his girlfriend works, he is pushing the door in. When the camera angle switches he is pulling the door open.
Continuity mistake: Carrie says that Deacon does not "drink or smoke." Previous episodes have shown him drinking beer with the guys. Also, in the episode "Friender Bender", it was mentioned that he drank a margarita during dinner at a restaurant.
Continuity mistake: Doug goes to Deacon's to tell him about Kelly wanting to get back together. Deacon is putting on his shoes and in different shots, sometimes his shoe is almost on and then other shots it shows him holding it in his hand about to put it on again.
Other mistake: Carrie says that Deacon doesn't drink or smoke. Many episodes have shown Deacon drinking a beer or a margarita.
Other mistake: During the picnic softball scene, there are mountains in the distance. There are no mountains in or near Queens New York. (00:05:40)
Visible crew/equipment: When Carrie walks in and sees Hollie for the first time in the episode, a boom mic can be seen following Carrie across the kitchen. (00:07:00)
Visible crew/equipment: When Carrie goes into the kitchen and Doug is seen through the window getting burnt, the boom's shadow can be seen moving along the wall by the window. (00:14:45)
Character mistake: In the opening scene, Doug call Carrie "Kel" which is Deacon's wife. He calls her that when he's saying they should just get a new grill.
Thanks Man - S6-E9
Other mistake: When Deacon's youngest son says "is that man going to freeze, daddy" you can see the older son mouthing the lines. (00:06:16)
Continuity mistake: While Arthur tries to convince Spence about the card, when Spence bites into the fake cookie he's holding it in his left hand and holding the plate in his right hand, but in the next shot facing Arthur the items have switched hands. (00:16:30)
Continuity mistake: In this flashback episode, when Doug is shaving his mustache and talking to Deacon by his locker at IPS, Danny Heffernan's name can be seen on a locker. At this time, Danny was not working at IPS.
Cheap Saks - S6-E15
Continuity mistake: At the art gallery, the way Doug is holding the program instantly changes a couple times; arms crossed/uncrossed, program folded/unfolded. (00:02:20)
Cheap Saks - S6-E15
Visible crew/equipment: While Doug reaches for the phone when Trish is calling you can see where the kitchen wall is ending on the set. (00:11:53)
Cheap Saks - S6-E15
Continuity mistake: Near the end of this episode, after Trish Flintoff leaves, Doug is telling Carrie and Holly that she's a nice person. Doug is looking at Carrie, then the shot changes and he is immediately looking down and reaching towards his back pocket. It also looks like he's trying not to laugh. (00:19:35)
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.