The monthly business survey, taken midway through the month, found the diffusion index of manufacturing activity remained positive, but dropped from 12.5 to 8.5.
Although growth slowed, the index has shown significant improvement since August, when the diffusion index stood at minus 30.7.
In April, the index for new orders and shipments each fell 1 point and remain "at relatively low readings," the Fed said.
The index for unfilled orders, concurrently, rose dramatically, climbing 14 points to move into positive territory.
This suggests "a backlog of unfilled orders," the report said.
In the report, numbers below zero indicate a contraction, while numbers above zero indicate growth.
In April, 27 percent of the firms responding to the survey indicated employment at their company was increasing, while 9 percent indicated employment was declining. The average number of work hours in the month was unchanged with 75 percent of firms reporting no change in their work week.