iAd is killing the performance of my app

I've developed an app for iOS with Swift and now I'd like to add an ADBannerView in my tableviewcontroller just to show some iAd banners. This is what I did :

I linked the iAd framework
In the ViewDidLoad of my tableviewcontroller I have added the following code :

self.canDisplayBannerAds = true

Quite easy! Perhaps too easy, because everything seemed to work fine, the view displayed the ad correctly but... performance was really bad!! My tableview scrolls smooth if I don't show the ad and keeps lagging while the ad is displayed... how come? What have I missed?

Thanks a lot

Solution

thanks for your help, I was totally wrong, iAd wasn't the cause of slowness of my app.

I've found the problem (I was setting the font of a textbox inside the cellforrowatindexpath method).

I've upvoted your comments because they were the correct way to find the issue.

thanks again All the best