Earlier in March Google had introduced Google AdSense Ad Review Center to some selected accounts, which gives you more transparency and control, and ensures that ads are relevant to your site's content and users. This feature is now available for all publishers, utilizing placement-targeted. You can get started with this feature by visiting your 'Competitive Ad Filter' page, located under the 'AdSense Setup' tab.

[…]Before getting started, we strongly recommend keeping your review preference set to the default of 'Run ads immediately.' This will let you allow or block ads after they have run. If you choose the other option of 'Hold ads,' the ads will await review for 24 hours before being allowed to run automatically. Using the 'Hold ads' setting will keep ads from participating in the auction while they await review, potentially lowering winning bids and your AdSense earnings. Ads that you have blocked can't compete in the auction either, so we ask that you keep in mind the revenue impact of blocking ads or switching from the 'Run ads immediately' setting.[…]

Google, AdSense, Online Advertising, Online Ads, AdSense Features, Ad Filter