Research firm IDC is out today with preliminary data from its quarterly study tracking worldwide tablet market share putting Apple at 40% market share compared to Android’s 56.5% of the market in Q1 2013. In the year ago quarter, Apple held 58.1% of the market surpassing Android’s 39.4%. IDC says Android shipments were increased thanks to strong growth of Samsung’s smaller sized tablets, while ASUS moved into the number 3 spot with 350.0% year over year growth due to strong demand for the Nexus 7:

ASUS managed to move into the number 3 vendor spot as it continued to see decent tablet shipment demand from the highly marketed Nexus 7 device. But, with Google’s I/O conference right around the corner and expectations of an imminent device refresh, the company will need to find a way to sustain its momentum. Amazon fell to the number 4 position, once again the victim of a highly seasonal product cycle.

Despite Apple taking number two behind Android for tablet shipments by operating system, it remains the top vendor by OEM taking a 39.6% share of the market vs Samsung’s 17.9% and 5.5% for ASUS. IDC notes that Apple actually exceeded expectations for Q1, where it typically experiences a drop off in shipments, by selling 19.5 million units compared to a forecast of 18.7 million:

The company, which historically has experienced a steep drop off in first quarter shipments (following strong holiday sales in the fourth quarter), saw some smoothing of that seasonality this year. Number two vendor Samsung also performed above expectations and managed to grow its shipments over the fourth quarter as more of the company’s smaller-sized tablets began to gain traction in the market. Samsung has also used its recent Android smartphone growth to help bring its tablet product line into new markets and channels, leveraging the opportunity to package and bundle. The strong performance of the two market leaders helped drive total shipments to an impressive 49.2 million units for the quarter.

As we often warn with these kind of reports, shipments include “shipments to distribution channels or end users,” so it’s not necessarily an accurate representation of sales to customers as not all vendors provide that information.