To extend your wife visa:

1. Take your passport copy with visa stamped page and your ID copy.

2. Take your wife passport copy and ID of your wife.

3. Take evidence document for your wife delivery or pregnency from the doctor from your native place.

4. Take visa extension fees of Qrs.500

5. Take all the documents and money and go to the Airport emigration department (located at the Back side of the parking area). One counter (i think it is the last counter) is there for submitting the documents for visa extension and submit the document with fees(Qrs.500)

They will make the extension of visa online. So that your can enter qatar within next six months(Provided the actual visa in her passport is more than six months period)