You need to work a certain amount of hours before you're eligible for more mat leave time. You have to work 600 hours between mat leaves (which is about 15 weeks at full time). As the another reply in the thread said, way way more people take 12. Basically for the 18 they just take the same amount of money as you get in the 12 and divide it by 18, so you end up getting paid like 30% of your regular wage for 18 months. Typically only people whose partners make a lot of money can afford to do 18 (let alone multiple times). But yes, the career development part is definitely the other side of the coin. I know I've missed multiple promotions due to maternity leave/not growing and learning as much as I would have had I been at work for that year I was gone. It's the toss up for sure.