When I was in the EU, I knew a woman who had 4 kids, each ~1/1.5 year appart. So she would have a kid, be out 6 month, go back to work for 6 month, have another kid, rinse and repeat 4 times :) .
It was a total nightmare for her employer because they couldn't let her go, and they couldn't hire anyone permanently to do her job. They could only use short term contractors who would stay 6 months (barely enough time to get up to speed) and then leave. I don't know if she was "abusing" the system, I mean, it was her right by law to do that, but after popping the 4th one she left work to be a stay at home mom. I don't know how well her employer took it :)