This study assesses the results of a mandatory blended learning-program for counselors (e.g. midwives, sonographers, obstetricians) guiding national implementation of the Non-Invasive Prenatal Test (NIPT). We assessed counselors' 1) knowledge about prenatal aneuploidy screening, 2) factors associated with their knowledge (e.g. counselors' characteristics, attitudes towards NIPT), and 3) counselors' attitudes regarding the blended learning. A cross-sectional online pretest-posttest implementation survey was sent to all 2,813 Dutch prenatal counselors. Multivariate linear regression analyses were performed to identify associations between counselors' knowledge and e.g. their professional backgrounds, work experience and attitudes towards NIPT. At T0 and T1 1,635 and 913 counselors completed the survey, respectively. Overall results show an increased mean number of correct answered knowledge questions; 23/35 (66%) items at T0 and 28/37 (76%) items at T1. Knowledge gaps on highly specific topics remained. Work experience and secondary care work-setting were positively associated with a higher level of knowledge. Most counselors (74%) showed positive attitudes towards the blended learning program. The mandatory blended learning, along with learning by experience through implementation of NIPT, has facilitated an increase in counselors' knowledge and was well received. New implementations in healthcare may benefit from requiring blended learning for healthcare providers, especially if tailored to professionals' learning goals.