In 1982 he became Director of the Wilson Genetics Center at The GW University. Dr. Larsen has been an active member of the American Congress of Obstetricians and Gynecologists. He was promoted to Professor in 1986.
Dr. Larsen specializes in high risk pregnancy care with special interest in prenatal genetic screening and diagnosis. In 1976 he became the leader of the prenatal genetics program at The GWU and started performing amniocentesis. In 1984 he introduced the technique of chorionic villi sampling (CVS) to the Washington DC area.
He has published on prenatal genetic screening and on perinatal infections. He has helped establish national guidelines for the diagnosis and management of Group B Streptococcus infection in pregnancy.