Ashley May | USA TODAY

Buzz60

Matt Sayles, AP

Another reason to forget middle children: Americans have stopped having them.

Ahead of National Middle Child Day (it’s Aug. 12, if you forgot), women's lifestyle magazine The Cut points out that middle children could go extinct.

The Sue Hecks and Jan Bradys of the world are becoming a rarity, as family planning trends from the 1970s have essentially reversed.

In 1971, three children was ideal, Pew Research Center notes, citing Gallup data. In the late '70s, more than 35 percent of moms between 40 and 44 had four or more children and just 22 percent had two children.

Fast forward to a 2014, where Americans now say two children is best, and only 12 percent of women in their early 40s have four or more children. U.S. birth rates declined last year for women in their teens, 20s and their 30s, leading to the fewest babies in 30 years, according to a government report released in May.

The average cost of raising a child might contribute to the trend, Pew suggests. In 1960, the cost of raising a child was about $198,560. In 2013, it shot up to $245,340.

Some couples who do have three children fit into a rare category of wealth, a 2014 New York Times piece suggests. More money equals a greater probability of a middle child.

Experts also point to shifting attitudes about family life among Millennials, who are more inclined to delay childbirth. If data on Generation Z proves true, this trend is likely to continue.