Visible crew/equipment: During Spence and Danny's fight scene, there are a couple of shots where you can see Danny's mic pack on his belt. (00:16:20)
Visible crew/equipment: When Fisker comes down to the drivers area of IPS, there is a white T Mark on the floor. (00:14:20)
Visible crew/equipment: When Doug gets the beach ball, all the stage lights are reflected in it. (00:14:00)
Visible crew/equipment: When Carrie notices that Doug has walked out the room, there are some tape markers on the floor from where Doug was stood. (00:09:40)
Strike One - S3-E5
Visible crew/equipment: When Carrie is trying to return the truck, there are tape markers visible on the floor. They are little white dots. (00:11:35)
Visible crew/equipment: When the dummy is on the sofa with Arthur, the stage lights are reflected in its sunglasses. (00:16:00)
Visible crew/equipment: When Arthur is saying about how someone should be able to go out their house and turn left or right, he looks up and the top of the set and the set lights are visible in his glasses. (00:02:45)
Visible crew/equipment: When Doug is talking on the phone, the shadow of a boom mic moves on the wall behind him. (00:00:20)
Visible crew/equipment: When Doug is lying on the floor with the phone on him, the camera zooms in and you can see a boom arm reflected in the phone. (00:19:35)
Strike One - S3-E5
Visible crew/equipment: When Doug is listing all the extras for the truck, you can see tape markers on the floor behind them. Specifically, one in between the feet of an extra that is standing behind them. (00:08:50)
Visible crew/equipment: When Doug is outside talking to Deacon and Arthur opens the kitchen door, as the door swings back you can see all the set lights reflected in the glass. (00:08:20)
Visible crew/equipment: When Doug sneaks out of Carrie's house and finds her having a cigarette by the car, a boom mic shadow can be seen on the bush beside Doug. (02:53:45)
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.