Talk to Gynecologist on Pregnancy - Chromosome Profile Test

Aoa, we are here in Germany and my wife is 12 weeks pregnant. Doctor suggested us to take chromosome profile test to detect any disorder in baby. At first, she said, it is not must to do but when I told her, we are first cousin from mother's side, she said better take it as there could be 15 to 20% chance. How important is for us to take this test because we are first cousin's and test is quite expensive here? Kindly enlighten us. My wife is 24 and I'm 30. Thank you.