H1 To H4 To H1B again

[RR12]

My H1B- I 94 expired in January 2018. I applied for H4 which has been approved. Meanwhile I got an offer from a company who are ready to do COS and apply for H1B extension based on approved I-140. Currently I am 5 months pregnant and I believe I might get H1B approval during/after my 8th month. 

a. If that does happen, am I required by law to join the company immediately on H1B approval? 

b. If not, can I join 2 months after my delivery and H1B approval without impacting my legal status (since my joining is flexible). 

PS: I am in dilemma as I would very much like to work but I do not want to stress myself at this time worrying about my H1B legal status in case I am required by law to join a company as soon as COS goes through. 

[pontevecchio]

Do you think this is the only job offer you will get? Deal with the pregnancy and birth and THEN look for a H1 job.