Can I fire a pregnant construction executive for poor attendance if her absences are related to her pregnancy?

A pregnant employee is entitled to take leave under the FMLA, if the law covers your business and the employee. If her time off is medically necessary, she is entitled to take up to twelve weeks of leave per year; this leave is unpaid.
Your own policies may also require pregnancy leave. You must treat employees who are temporarily unable to work because of pregnancy just as you treat employees who are temporarily disabled for other reasons. So if you offer paid temporary disability leave, or if you customarily allow employees who are unable to work for a short period of time to take paid leave, you must offer this leave to pregnant employees as well.
By the same token, you do not have to treat a pregnant employee any better than other employees. It is illegal to fire an employee because she is pregnant. But if you would fire any employee whose attendance record was as poor, you may legally fire your employee.