Apple shipped approximately 3.9 million Apple Watches in the September quarter, according to new IDC research estimates for the wearables market published on Thursday.

The figure is up slightly from the 3.6 million IDC suggested for the June quarter, and gives Apple an 18.6 percent marketshare. The growth is credited to Apple introducing the Watch to new countries, as well as finally bringing the product to third-party retailers.

The public has mostly been interested in cheaper Sport models of the device, explaining Apple's decision to introduce new gold and rose gold color options in September, IDC said.

Leading the wearables market in the quarter was Fitbit, which shipped 4.7 million fitness trackers thanks to expanding international demand, and corporate purchases meant to reduce sick days and healthcare costs. Target, for instance, ordered 335,000 units for its workforce.

Xiaomi ranked third at 3.7 million units, while Garmin and XTC (under BBK) trailed well behind at just 900,000 and 700,000 units, respectively. Garmin's position is reportedly linked to its focus on serious fitness enthusiasts, while XTC has just one product and sells only to China.