You’d cause a baby boom prior to and at the end of the moratorium. If you were possibly considering having kids, and some totalitarian state was capable of enforcing such a rule, you’d breed before. And if you didn’t have a chance before, and thought they could enforce another moratorium after, then you’d breed as soon as you could when the moratorium ended. The longer the moratorium, the bigger the incentive to breed while you can.
Which would cause a concentrated increase in resource requirements associated with both the before moratorium and after moratorium baby boom, which would carry on through the subsequent decades as these generations aged.
You’d be introducing a problematic pulse in population to the problem of population, and most likely not making any real dent in population growth….oh and adding a whole bunch of other additional problems to society (enforcement?, infanticide, etc…).