The waiting room at Mary's Center in Washington, DC on February 24, 2014. Mary's Center is a non-profit health center for the underserved, uninsured or underinsured.

The percentage of U.S. adults without health insurance reached a four-year high in the last quarter of 2018, but was still well below the peak level seen before Medicaid expansion under the Affordable Care Act in 2014, a new Gallup survey published Wednesday found.

The national uninsured rate climbed to 13.7 percent in the fourth quarter of 2018, its highest level since the first quarter of 2014 when the rate reached 13.4 percent, according to data the compiled from Gallup. Women and adults under the age of 35 reported among the highest rates without insurance at 12.8 percent and 21.6 percent, respectively, the survey found.

The number of people lacking insurance reached its highest point in the third quarter of 2013 at 18 percent and steadily improved over the next three years, according to Gallup, which has been tracking uninsured rates since 2008. But the uninsured rate has been on the rise every quarter since the last two quarters of 2016 when Donald Trump was elected president.

Uninsured rates rose by more than 3 percentage points across the West, Midwest and Southern regions of the U.S. while the rate along the East was effectively unchanged.

Gallup's numbers are based on a 28,000 sample size of randomly selected U.S. adults. The data is collected as part of the Gallup National Health and Well-Being Index.