If you're about 13 weeks now, you have time. I'd call the OB back tomorrow and ask for a referral to a genetic counsellor. Or call your state genetics service and ask for one. They're based at the main hospitals. In Victoria, it's VCGS.

An amnio can be done at any time up to birth. You may decide to wait to have a morphology scan first to see if something else is picked up. Or you may decide you'd rather know for sure sooner than later.

If you do have an amnio, ensure it's done by an expert OB who specialises in perinatal diagnoses. The general risk of miscarriage from an amnio is about 1 in 500. The experts should have a much lower risk.