H1B approved but can not work as due date is in Jan

I have an approved H1b which is effective from oct 15th 2013. But I am pregnant and can not work by Feb end as due date is in Jan. So my employer is delaying the SSN application so that the idle period can be covered by leaves. I have not started working till now and the idle period will be almost 4 months. Please advice how the idle period should be compensated so that it does not affect my COS.