What Are The Risks Of Having A Miscarriage At 19 Weeks With Amniocentesis?

My step daughter is 19wks pregnant . She had a blood test at 9 wks showing a risk of downs/genetic disorder of 1:700 -she is 32yrs old . A nuchal scan was normal the next day .A panorama test (?) was inconclusive so repeated on dads buccal mucosa and was okayShe had the blood test repeated and now told risk is 1;200 and has been recommended to have an amniocentesis . This is her third pregnancy .She lost twins in her first pregnancy -trisomy 16 .She had vaginal bleeding at 16wks thought to be a subchorionic bleed How significant is the increase in risk and what are the risks of her miscarrying at 19wks with the amniocentesis ?