What would happen if people had to apply for permits to become parents?

We have to apply for the right to do so many things in this country;build, drive, vote, get a loan, etc. Why is is that everyone can become a parent? I wonder what would happen if we were able to (impermanently) sterilize everyone at birth, and only granted them fertility later in life if they were deemed fit. I am not talking about all out eugenics here, but people would have to meet a few requirements. These requirements would include mental stability, some level of financial stability, and probably a minimum age. I think this would reduce the number of unwanted children, as well as lower the incidence of child abuse. I also wonder if it would reduce some of the stresses caused by an ever ballooning world population. However, I can see some possible downsides; infanticide of the unwanted , unlawful discrimination, etc. I just wanted to know what everyone else though of the idea, or if anyone has other solutions