Prenetal diagnosis of Down Syndrome is by

Prenatal diagnosis of down syndrome can be done by all the above. Fetal ultrasonography or nuchal translucency scan is done in the first trimester. Triple test using alpha fetoprotein,unconjugated estriol and beta hCG helps in 2nd trimester also helps to detect down syndrome. Karyotyping helps to locate 3 copies of chromosome 21. Reference: Nelson TB of pediatrics 19th edition, pg 402