20 week scan of my baby boy

So the nurse so extra fluid then normal in his kidneys so the fact that I'm 40 years thay did a special test because I'm over 35 came back good so now he asking to test again with a needle threw my stomach that may cause miscarriage but if the blood tests came back okay why would you test it again and cause problems i told him no im trusting in God so did anybody go through this over 35-40 the test was for a Down syndrome and I will problems because I'm older