While I agree that overpopulation is a huge problem, there's a flaw in your plan.
By mandating abortion in general or by those with an IQ of less than average presents a couple problems.
As builder already stated, the "ideal" couple who is wealthy and intelligent does not guarantee an ideal child.
Not only that, we are almost heading into a problem. If simply produce children of white-collar quality who all want to be a scientist or teacher, who is going to do the blue-collar work? In some parts of Ontario, there are labour shortages because - believe it or not - there are TOO many young adults that are educated and are persuing suit & tie jobs.
I'm not saying it takes an uneducated person, or an idiot, to have a job in trade or labour, but because education is prestigious and valued, more people want it.
By aborting fetuses that we deem to be "unsuccessful," we may actually contribute to a shrinking labour/trade/blue collar population, and that is ultimately bad for the economy.
We could do something like China does - one child per family unit. Of course that runs into problems like couples not being happy with what they get on their first shot. I'd like to think we're more civilized than the average Chinese person and won't kill off a baby and bury it in the ground because it's a girl, and so that the government won't notice.
After that one child is born, a surgical procedure should take place immediately after on the male (because it usually reversible) so that the same couple cannot reproduce.
I don't know if I really condone what I'm saying, but I think what I propose is a better alternative to mass aborting of babies.
