Kate Middleton is known for setting trends with her outfit selections.

But she’s really bucking the current societal patterns with her announcement today: She and Prince William are expecting their second child.

In the United States today, the average birth rate per woman is 1.9, according to The Heritage Foundation’s 2014 Index of Culture and Opportunity. The rate is roughly the same in the United Kingdom, according to the World Bank.

>>> Chart: How  the Fertility Rate Has Dropped in the Past 10 Years

Western countries face a slew of economic consequences because of declining birthrates. Shrinking workforces will affect economic prosperity, and the eventual large population of the elderly will anticipate government programs providing the assistance they’ve been promised – despite the fact that the pool of taxpayers won’t be what it once was.

But the consequences go beyond the economic.

First, plenty of Americans would like to have more children than they actually do ultimately have: A 2013 Gallup poll found that Americans wanted an average of 2.6 children – significantly higher than reality.

According to the poll, the top reason cited for not having more children was concern about the cost, with 65 percent mentioning it. (Let’s face it: being British royalty has its problems, but lack of cash flow isn’t one of them.)

Prince George in the arms of his mother the Duchess of Cambridge (Photo: Newscom)

Prince George in the arms of his mother the Duchess of Cambridge (Photo: Newscom)

In contrast, only 6 percent attributed fewer children to “personal choice” or “no desire for children.”

But there’s also the fact that an increasing number of children grow up without brothers and sisters. As someone who grew up with four brothers and sisters, I definitely had my moments of fantasizing about the life of an only child – particularly when a sibling just wouldn’t stop bothering me, or when I wanted to kick out my two sisters (who I shared a room with) and have some peace and quiet.

Yet I also have plenty of good memories, from the five of us building blanket “forts” in the living room to bursting into tears over something in my twenties – and realizing that my “baby” sister was grown-up enough now to comfort me, not vice versa.

You shouldn’t need to be royalty to have the “luxury” of a second child – or third, fourth, or well, à la Duggar, 19th. Let’s hope that Kate Middleton’s ability to set trends includes family size as well as fashion.