I'm not sure about this either...this is really something that a genetic counselor rather than your ob or a nurse would be able to answer best. Call your ob and ask for a referral to their genetic counselor.
Im not sure, but i suggest you call your OB and speak to him/her and have them explain it to you so that you understand it better. Im a nurse myself and i never speak to the nurse at my OB's office, i always request to speak to my doctor who is suppose to have a better understanding than the nurse and should be the one explaining it to you, what if you have questions. Take care and just give them a ring.