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)

Hungry Man - S1-E21
Continuity mistake: At the very end when Carrie walks out the level of foam on Doug's beer bottle changes between shots. (00:21:20)
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.