Can you be terminated from a job for becoming pregnant.

Pregnancy is not a 'disability' under the Americans with Disability Act. If you aren't able to perform all of the essential functions of your job, you wouldn't qualify for the ADA anyway. However, if your employer has a policy of accommodating other non-ADA eligible employees with 'injuries' (apart from 'light duty' to workers compensation recipients, which I'll discuss below), then they would have an obligation to accommodate you or it would constitute 'pregnancy discrimination' which is prohibited by law.

Ordinarily, 'light duty' is something an employer provides to those on workers compensation in an effort to reduce benefits payments (and therefore insurance premiums). It is not generally a matter of right, just something employers do to cut costs.

If you are able to perform all of the essential functions of your job despite the pregnancy, and are still being discriminated against, that would also be unlawful.