Samsung grabbed tablet market share from Apple during the first quarter of this year, but the iPad maker retained the top spot in an otherwise slowing tablet market.

Worldwide tablet shipments totaled 50.4 million units during the quarter, increasing by just 3.9% compared to the same quarter a year ago, according to an IDC study released yesterday. The shipments rose at a slower rate than expected by IDC, which said the tablet category could struggle this year.

Apple earlier this month reported a year-over-year quarterly drop in iPad shipments, and IDC's study reflected similar results. IDC counted Apple's iPad shipments as totaling 16.4 million during the first quarter, a drop of 16.1% compared to the same quarter the previous year. Second-place Samsung's year-over-year shipments rose by 32% to 11.2 million units.

IDC's tablet shipment numbers also include "2-in-1" PCs, which are hybrids that can be both tablets and laptops. Many of these computers typically have Windows 8 and detachable screens that turn into tablets.

Consumers are holding on to existing tablets and not upgrading, and large-screen phones - also called "phablets" - are becoming more popular, said Tom Mainelli, IDC's vice president for devices and displays research.

Tablet shipments in the first quarter were otherwise a mixed bag for vendors. Lenovo, which was the fourth largest tablet vendor, recorded a whopping growth rate of 224.3% in shipments, totalling 2.1 million units. Lenovo meanwhile is catching up with third-place Acer, whose shipments dropped by 2.8% to 2.5 million. Shipments for the once fast-growing Amazon dropped by 47.1% to 1 million for the quarter.

Android was the dominant OS, grabbing roughly 66% of the market share, IDC said. Hybrids are helping Windows 8 gain tablet market share, especially among people who need PC-like functionality inside a tablet, IDC said. But the market share for Windows remains small, IDC said.