American women are having their first babies at increasingly older ages.

According to a recent report from the National Center for Health Statistics, the average age of first-time mothers in 2014 was 26.3, up from 24.9 in 2000. The sharpest increases in age have occurred since 2009, when the average was 25.2. But there has been a steady rise over the past four decades: in 1970, the mean age of a first-time mother stood at 21.4.

The main reasons for the uptick: the decline of first births among teenagers and the increase of first births among women over age 30. Over the 14-year period examined, the proportion of first births to women younger than 20 declined 42 percent, while rising 28 percent among women ages 30 to 34 and 23 percent among women 35 and older.

Asian or Pacific Islander mothers had the oldest average age at first birth, 29.5, and American Indians or Alaskan Natives had the youngest, 23.1. Still, the average age has increased across all races and ethnicities.

At the same time, the average age increased in every state and the District of Columbia. The largest increases — 1.7 years or more — were noted in California, Oregon, Washington, Utah, Colorado and Illinois. Among the states with the smallest increases were Vermont, New Hampshire, Massachusetts, Kentucky and Tennessee.