Given the high-ratings and constantly mounting buzz for Shonda Rhimes' political thriller, it's more than likely that Kerry Washington's pregnancy is the reason for the reduced order—especially since producers will not be working her pregnancy into the show.
Rhimes is also known for running a tight ship in terms of storylines, rather than letting episodes roll by solely in order to stretch out plots and hit syndication quickly. In an interview with Vulture, Rhimes divulged that the Harrison-Adnan Salif storyline that appeared in episode six was actually supposed to come later in the season, but producers realized that episode six was lacking story and they moved it up sooner. While reducing an episode order from a network simply for story isn't a small feat, superstar executive producers like Rhimes do have the sway to make such decisions happen, especially for the sake of story.
While it's refreshing that ABC isn't going to force Olivia Pope into even boxier coats and stuff her behind a desk and pillows when her bump gets too hard to hide, raise your hand if you're a little sad that this means Fitz and Liv's jam-making, child-rearing Vermont life is now that much further away.