A steep slide in UnitedHealth Group shares was dragging on the Dow Jones Industrial Average on Thursday, putting the blue-chip index on track for historical underperformance versus the S&P 500.

The UnitedHealth slide weighed heavily on the Dow, which fell 500 points, or 1.3%, Thursday morning.

UnitedHealth weighed heavily on the Dow, falling nearly 23% after reporting adjusted first-quarter earnings of $7.20 per share on $109.58 billion in revenue, missing analyst expectations. The insurer also lowered its full-year earnings guidance,