WASHINGTON — The median price of a house or a condo that sold in the D.C. metro in October was up 2.9 percent from October 2017, according to a monthly S&P/Case-Shiller Home Price Index, the smallest annual gain in median prices among the nation’s 20 largest cities.

The average annual gain in the 20 largest cities as of October was 5 percent. The year-over-year change nationwide in October was 5.5 percent.

It is the third consecutive month that the rate of home prices increases has slowed across the country.

Rising home values are back in the cards for Las Vegas, one of the hardest-hit housing markets during the start of the great recession. The median price in Vegas in October was up 12.8 percent from a year ago, the biggest annual gain in the nation.

“After the last recession, Las Vegas diversified its economy by adding a medical school, becoming a regional center for health care, and attracting high technology employers. Employment is increasing 3 percent annually, twice as fast as the national rate,” said David Blitzer, chairman of the Index Committee at S&P Dow Jones.

After Las Vegas, San Francisco ranks No. 2 for annual home prices gains, up 7.9 percent as of October. Phoenix knocked Seattle out of the top three, with an annual price gain of 7.7 percent.

New York City joins the D.C. region at the bottom of the list for annual gains in home values among big cities, up 3.1 percent as of October.