According to the recent numbers from Strategy Analytics (via AppleInsider), it seems that in Q4 2018, Apple had managed to ship as many as 9.2 million Apple Watches. Note that these are shipped figures, meaning that the actual number of units sold could be less, but since Apple probably as a good handle on the demand for the wearable, it could be close.
The shipment of 9.2 million also meant that Apple had managed to capture 50.7% of the market. However according to Strategy Analytics, 50.7% is actually a lot less than the previous year in 2017 where Apple reportedly commanded 60.4% of the smartwatch market. The closest company on that list is Fitbit who is sitting at 12.2%, which is actually a remarkable jump considering that in 2017 the company was at 1.7%. Samsung also seems to have managed to increase their market share from 10.6% to 11.8%.
Despite Apple seemingly losing a bit of market share, they are still very much in the lead. With various stories about how the Apple Watch has been saving lives with its new features, we imagine that this could help spur sales further.