ALEXANDRIA, Va. — Bedding sales fell in March, with unit sales dipping 1.7% from the same month a year earlier and the wholesale dollar value of bedding shipments dropping 3.3%, a sample of large producers indicated.

There was a March surprise: The innerspring category gained market share as specialty sleep slumped.

The March Bedding Barometer report, issued by the International Sleep Products Assn., provided more bad news for an industry that has been mired in a sales slump. For the first quarter of this year, bedding units are down 3.2% and the wholesale dollar value of shipments is off 3.3%, ISPA said.

The latest report, which reflects the performance of 16 bedding producers that account for a majority of industry sales and shipments, brings bad news for the specialty sleep segment, traditionally a strong performer.

In March, specialty mattress units dropped 14.8%, compared to a 0.1% unit gain for innerspring mattresses. The dollar value of specialty mattresses plunged 16.3% in March, while it rose 5.4% for innerspring mattresses.

The average unit price of innerspring mattresses rose 5.3% in March, to $251.90, while the average unit price of specialty mattresses fell 1.7% to $778.36.

For the first quarter, innerspring mattress units declined 2.9%, while innerspring mattress dollars were up 0.5%. Specialty mattress units were down 3.9% in the quarter and the dollar value of shipments declined 5.1%.

The average unit price for innerspring mattresses rose 3.5% to $254.68, while it dropped 1.3% to $764.08 for specialty mattresses, ISPA said. Overall, the average unit price dropped 0.1% in the first quarter, to $211.89.

The Bedding Barometer reports reflect the performance of mattress producers that in 2011 accounted for 66% of total units and about 76% of the total dollar volume of bedding shipments.

ISPA cautions that the performance of this sample of companies may not reflect the performance of the full mattress industry because of market share or distribution shifts.

But the monthly reports are followed closely within the industry and by analysts who track industry trends.