There has been a few question about how this works in other countries. This is how it works in Norway:
The total parental leave is 47 weeks at 100 % pay, or 57 weeks at 80%. 10 weeks are earmarked for each parent, the remaining 27-37 weeks can be allocated as the parents wish.
While you are on leave, your pay is being paid by the government, not your employer.
Your employer will normally replace you with someone on a time-limited contract. In Norway, there are a lot of legal protections for workers, and this means the hiring process is very conservative. It is inordinately hard to get your first job after graduation. However, time-limited positions to cover for maternity leave is less of a risk for employers, and it is traditionally how you get your first job and references. Since the replacement is normally brand new, they’ll cost less in terms of wages.
The manager should have had a few months to prepare before the pregnant worker goes out on leave. Any manager who has a problem ensuring a smooth transition with months to prepare should not be a manager. This is an essential area of competence.
As an investment, this is generally considered to yield gigantic returns financially.
Making it easier to have kids and return to the workforce ensurers that more women do return to the workforce and spend a few more decades as taxpayers, being massive assets. Growing up with employed parents who go to work every day makes it far more likely the kid will become a productive asset. (taxpayer).
Now, I made a back-of-the-envelope calculation on how much this is worth to us. Personal taxation is about 35 % of the government budget. Female employment is 74 %. In the US it is 62 %, so we are 12 % over. Thats an extra 6 % of the total labor force, and so represents 2 % of the budget.
In the US budget, a similar added income would be about 165 billion $, more than the yearly costs of the Iraq and Afghanistan wars.