Diagnosis of Congenital Syphilis Early congenital syphilis: Clinical evaluation; darkfield microscopy of lesions, placenta, or umbilical cord; serologic testing of mother and neonate; possibly cerebrospinal fluid (CSF) analysis Late congenital syphilis: Clinical evaluation, serologic testing of mother and child Early congenital syphilis Diagnosis of early congenital syphilis is usually suspected based on maternal serologic testing, which is routinely done early in pregnancy, and often repeated in the 3rd trimester and at delivery.