Corporate pension plans didn't see much good news in the month of April.

According to Wilshire Consulting, U.S. corporate pension plans' aggregate funded status fell by 0.1%, ending the month at 77.8% and bringing its year-to-date decline to 3.6%. The monthly change in funding, Wilshire said, was the result of offsetting increases in asset and liability values, while the year-to-date decrease was attributed to increasing liability values.

S&P 1500 companies saw a bigger drop, according to consultant Mercer, falling by one percent to hit 78% as of April 30. Mercer added that as of April 30, the estimated aggregate deficit of $504 billion rose by $12 billion, compared with the end of March. Funded status, it added, is now down by $100 billion from the $404 billion deficit measured at the end of 2015.