One interesting thing about birthrates that I think most people haven't really looked at is the data segregated by age groups.
In most countries with falling birthrates (save some exceptions like Japan) a huge part of this decrease is in the 15-25 age group. There is usually also a decline in the 25-29 but there's an increase or the same rates as we've had historically on the 30+ range.
What this mean is basically that we've eradicated teen pregnancy, and that's definitely something desirable in a developed society.
A sustainable population - not increasing just staying the same - requires each and every single female have more than 2 children on average.
Starting in your 30s, especially later 30s makes this extremely difficult. It takes months of perfectly hitting ovulation windows to get pregnant, and then you generally want at least ~9 months between children, so you're looking at ~2 years per child, all while fertility starts to rapidly decline as you head into your 40s.
The long and short is that a sustainable population is going to require the majority to start having children in their 20s. That figure going down has nothing to do with teen pregnancy.
As a peer alluded to, that's going to be for some ideal demographic in their twenties (probably early), hitting ovulation perfectly. Age changes things dramatically:
"Women younger than 30 have about a 20 percent chance of getting pregnant naturally each month. By age 40, the chance of pregnancy is about five percent each month." [1]
Things like IVF do not dramatically change the odds either. They're better of course, but it's far from guaranteed - it's still just a rather expensive roll of the dice.
Then on top of all of this, having children later greatly increases the chances of miscarriage, developmental issues (like Down syndrome) and so on.
Life's brutal here - you're in a race against time, yet the later you start the longer it takes, and the harder it becomes.
N=1 anecdata here, but... My wife and I got pregnant -- both times -- during the first month of trying. We were mid-30s, myself being 3 years older than she is, and my wife was old enough at the time of conception to have had a "geriatric uterus" and our first pregnancy, spontaneous fraternal twins, was considered "high-risk" out of the gate because of her age.
> Things like IVF do not dramatically change the odds either. They're better of course, but it's far from guaranteed - it's still just a rather expensive roll of the dice.
Sadly, literally all of our peers who were trying and having kids in the same demographic as us, +/- a few years, struggled hard and most needed fertility treatments. At least 2-3 of them were never able to conceive, despite the expensive and time-consuming treatments. It's brutal.
I will also add, I have a number of friends who are >= 10 years younger than I am and many of them also struggled with miscarriages in their late 20s while trying to start families.
No, if there is also a decline between the ages of 20-29 then the implication is not that we've eradicated teen pregnancy. It's that people are not having as many kids. When you have kids in your 20s you can have more than if you start in your 30s
Working a minimum wage could buy a starter home "back then". It now can hardly pay rent, and starter homes essentially no longer exist, even if someone wanted one.
In most countries with falling birthrates (save some exceptions like Japan) a huge part of this decrease is in the 15-25 age group. There is usually also a decline in the 25-29 but there's an increase or the same rates as we've had historically on the 30+ range.
What this mean is basically that we've eradicated teen pregnancy, and that's definitely something desirable in a developed society.