What is 2nd Trimester Screening - Usually who miss the 1st Trimester screening they can come back for the 2nd trimester screening. Which is usually done between 16 weeks to 18 weeks. 16 weeks we do the quadruple marker in this the Maternal Harmon's are been taken which is Beta HCG.The second trimester scan is a routine ultrasound examination in many countries that is primarily used to assess fetal anatomy and detect the presence of any fetal anomalies.