We don't control who comes here with childbirth, it's actually a far less controllable method. Immigration can have totally arbitrary rules, and until the world

We don't control who comes here with childbirth, it's actually a far less controllable method. Immigration can have totally arbitrary rules, and until the world hits 11bn and wealth is equalised there will be an unlimited supply of immigration. Men aren't forced not to take time off in most countries but they still generally choose not to. There are multiple ways to address the perceived gender pay gap effect of maternity leave, the most obvious is to have state funded (m|p)aternity leave. The alternative, in countries other than the US with very long maternity leaves, is to shorten it. If women aren't allowed to take 9 months off paid then there won't be any discrimination on that basis.