NT scan normal, dualmarker test positive

Sir, My wife is getting pregnant, her age is 23. Now 14th week is going on. Last week we took NT scan and double marker test. Doctor said NT scan is normal, but the double marker test, trisomy21 is screen positive.  So he said, you take immediate decision and choose anyone option (amniocentesis, or NIPT). Doctor said NIPT 98% gives the correct result, But no guarantee for that result, amniocentesis is better, but it is a risk.  I asked to doctor, NT scan is normal, so what problem, is the double marker result is necessary. But he said, it is important. now What can I do at this time. Kindly help me, which one is better. He finally said, weeks going on. Take action immediately, otherwise if problem termination is critical. Please help me.