If you haven't already, I would go to a peri-natologist (not sure of the spelling - Mine was Dr. Sumner) and they can spell out the different scenarios of what the odds are of finding something vs. what the risk to the baby is, etc.
Before you go through a placental biopsy (CVS), there is a blood test (they'll prick of the finger to do 6 different dots to send off to a lab) they can do to let you know what the odds are of something genetic or chromosomal going on. I would wait for the results of that test before deciding on whether or not to go through with the CVS or an Amnio.
Keep in mind that with anything like CVS or Amnio, there's a chance of miscarriage or something happening to the baby (particularly with CVS - and again, the dr. can spell everything out). So factor that into the equation on whether or not to proceed with Amnio or CVS.
We had to make decisions like that too with both our daughters - because we had help conceiving, and they asked us about doing CVS or Amnio. We decided to do the blood test first, and would make any further decisions based on that info. Both or reproductive surgeon and OB/GYN supported our decisions to "not touch the baby" unless it was absolutely necessary.
Many prayers for you and your family in the meantime!