Could i be pregnant??

Patient: I recently received the depo birth control shot on Decemeber 19th 2014, I had unprotected sex a week before and have had after before the seven days of using a back up method using the “pull out” method all except on time which was before the shot on December 2014.. I am always regular with my periods every 28 days, however I am currently now four days late and took a test three days ago and it was negative could I still be pregnant even though I had the shot seeing as I was not using protection before the shot and before the shot had fully gotten into my system? I have read numerous places the shot it 98% effective and your chances of getting pregnant are very slim..

Symptoms: Late on period

Doctor: Hello,The depot shot is to be taken on day 1 of your menses and a back up method to followed for next 2 weeks hence. I f the injection is taken in the mid cycle without any menstrual bleed earlier ,then an unprotected sex a week before can definitely put you under risk of pregnancy. Also you must note that depot would cause stoppage of menses ideally in next 2 cycles and if you continue you will not have any menses. Thats the mechanism of action of depot injection.It is necessary to rule out pregnancy by a serum beta hcg level test, which if found to be raised will indicate pregnancy and if the levels are less than 1 , then you can safely assume that you are not pregnant.I hope i have answered your query in detail,wishing you good health,regards