Mommy found... she should wait to get rhogam.

I have negative blood.  My husband's is positive.  Apparently, if my baby has daddy's blood type, my body could attack my baby.

...

When I looked my doctor in the eye and asked him if he'd give his wife the shot he had just recommended to me, he paused.  And then in his indian accent he responded, "I can't tell you this as your doctor.  But, not now.  We'd choose to wait six more weeks, assuming no change in circumstances."

I had done my research.  But, as I'm not a scientist, and definitely not a doctor, I hadn't been able to really come up with an understanding of what the drug does.