I though when you join any company, is it suppose to be cover?
Maybe you can start to give the hint and inform your company few more weeks than you are pregnant. I notice some of the mummy know they are pregnant about 5 months.
Acccording the information from MOM, company only cannot terminate the pregnant women when the baby is more than 7 months.
For your case, it all depends how good is your boss and company.
Are you working in local company?