Imagine that in the 1950's the birth control pill was never discovered...even to this day it eludes the scientific community.
During that time frame, the population continued to boom and rose at unsustainable levels for generations. The infrastructure has finally reached its limit, and something HAS to be done. PSAs have been pumped through the airwaves for years about not having more than 1 child, but no legislation could ever pass to mandate it...or enforce it.
Sprinkle in some Idiocracy lore about the less desirable sections of society reproducing at alarming rates compared to the higher educated/higher earning sections. The population is quickly becoming dumber on average.
The extremely high levels of uneducated citizens increases the crime and poverty rates. Governmental programs meant to help lower-income families are strapped for cash and regularly decrease benefits as there simply isn't enough money to cover everyone.
A biotech company reveals to the government that they have produced and tested a chip implant that will help relieve the current population growth rate. This chip has been set at a default to render the individual, whether male or female, infertile until two requirements have been reached:
the patient is over the age of 25
the patient has an IQ level of 100 (average)
The hope is that all newborn babies will have the chip implanted (unknown to the parents) to help stop the unsustainable population growth. While this does nothing to deal with the current levels of people, it could stop the problem from continuing. Another option is that every hospital ends up with a 'Man in Black' that visits every patient (of child bearing age or younger) undergoing surgery and implants the chip, there by further decreasing the chances of unnecessary reproduction.
Is there any current day tech that would allow something along those lines...or something that could be considered close enough that a little handwavium could cover the gap?
It has not been stated that the chip works by changing hormone levels. I was originally thinking of it emitting some low level radiation of some sort to interfere with the organs or contraception. The body is capable of repairing damage from some types of radiation, as long as the levels are not above a certain threshold. I left out how the chip could work at first hoping someone would come up with an even better idea, but everyone seems to be stuck in only 1 possible solution.
Getting a microchip to tell time, is not even remotely an issue...getting it to determine IQ...or some other level of intelligence...is the hard part.