I think it'd be a heck of a lot easier to give maternity leave - you get pregnant on Mars, you go back to Earth and go through the pregnancy there, and as soon as the kid can stand space travel you go back home. Maybe you go back and the kid stays on Earth with the grandparents for a couple of years before heading out to Mars.
You get pregnant on Mars, it's too late.
Mars' surface is exposed to to 10-20 REM/year, about 30x what the NRC says is safe for a fetus, but even in a small colony you can tunnel into the omnipresent regolith to hide from it. Space around Mars orbit is exposed to 40-120 REM/year, and every millimeter of spacecraft shielding is painful to accelerate or decelerate.
With a large wealthy colony you could get around the radiation concerns (via cycler stations: you take a cramped and poorly-shielded but brief shuttle trip to the station and then you live in heavily-shielded relative comfort during the long transfer to Earth) but there's no getting around the orbital mechanics concerns: travel between Mars and Earth takes months. By the time you get to Earth your baby's long past the differentiating-blob-of-cells stage. In fact, if you wanted to take a cycler and you didn't time it right you might not even be able to make it to Earth before your due date.
If 1/3 gravity turns out to be insufficient for pregnancy then the best bet might be space stations in Mars orbit. Less delta-V for the shuttle to get there (and negligible delta-V use by the station itself) would make it cheaper, and the whole station could be a huge roomy centrifuge because you wouldn't have to worry about bearings like you do with a ground-based centrifuge. The station itself could be heavily shielded even more cheaply than a cycler (because the shielding likewise goes into a single stable orbit and stays there, but the orbit is easier to get to and maintain) - or, if we're doing any radiation remediation of Mars itself (I've seen studies of proposed EM radiation shield-generating satellite; it would take a big nuclear reactor but it wouldn't take magic) then space stations in low Mars orbit would share in the benefits.