Down Syndrome Check

Hi . . I am currently 15 weeks pregnant after 5 years and isn't my first pregnancy but don't know why for the first time , I feel so much of in need to do a down syndrome check . I don't care about checking on my other pregnancies but this time , I felt strong of the in need to check . Anyone has done the down syndrome check ? Able to share with me the experience ? What did doctor do to check , etc ? Result is close ?