再请教皮匠，863211： NIWEAD换专业。

Currently I am on H1B, also hold EAD based on NIW I 140 approvals. I used up the 6 years of H1B. My current H1B extension is based on NIW I485 pending. My NIW application claims are brain tumor research. Now I accept an offer as a medical resident in the next 4 years start from this July. My questions are
1 If I use EAD to complete my residency, how risky it will be that my I 485 was rejected?
2 How frequently the I485 will be checked? Is there any statistics?
3 How difficult to explain the similarity of my previous medical research and my current pathology medical residency?
4 If the tragedy of I 485 rejections happens, what should I do to save my life and residency in U.S.?
_(&)