According to an index of billing activity, architects ended the first quarter on an upswing, the American Institute of Architects said in a release. The organization's index registered 54.3 at the end of March, up from 50.7 in February. The index reflects the approximate nine- to 12-month lead time between architecture billings and construction spending. Any reading above 50 indicates an increase in billings. However, architects reported a slight decline in inquiries about new projects. On the billings front, architects in the Midwest led the nation with a score of 54.6. "We are moving into the busy season and firms are confident that they will remain busy throughout the spring," AIA Iowa Executive Director Jessica Reinert said in the release.