It is also a good idea to notify your employer in advance of your intended leave due to your pregnancy. Along with the Family and Medical Leave Act, your employer might provide leave as well. Ask in advance, and do so in writing, so you have a record of it.
However, your employer cannot force you to take leave. Some employers try to get their employees to leave during the later months of pregnancy. Often, this is unpaid leave. Your employer is obligated under law to allow you to work as long as you can perform your duties with reasonable accommodation. If your employer forces you to take leave, you can file a claim.