It has been estimated that 75% of infants born from mothers with active syphilitic infection will become infected in utero. Of those infected about one third will be symptomatic in the neonatal period and two thirds will have some symptoms within the first 2 years of life. However, it appears that the majority of patients with congenital syphilis are not diagnosed until late childhood or adolescence.

Congenital syphilis often gives a confusing serologic picture. Syphilitic infants usually have a positive RPR reaction. Sometimes, however, these infants have a nonreactive RPR result at birth, and the RPR responses may remain normal up to age 3 months before the titer begins rising. On the other hand, if the mother has a positive RPR reaction, even though she was adequately treated, many infants will have a positive RPR reaction due to passive transfer of maternal antibodies through the placenta. The same is true for the FTA-ABS test. However, if the VDRL or RPR titer of the infant is fourfold higher than that of the mother, this suggests congenital syphilis. Also, a fourfold or greater rising titer over the weeks or months after birth strongly suggests infection. To further confuse the picture, pregnancy is associated with an increased number of BFP reactions in the RPR, and reportedly, on occasion, even with the FTA-ABS. If the mother was adequately treated before delivery, the infant’s reactive RPR will revert to nonreactive without treatment in approximately 3-4 months. Cord blood may cause problems in neonatal syphilis testing due to possible contamination with maternal blood or false negative results caused by interference from hemoglobin or maternal infection very late in pregnancy. A modification of the FTA-ABS test that is specific for IgM antibodies is reported to detect and diagnose most cases of congenital syphilis in the newborn. However, reports indicate as many as 10% false positive results and as many as 35% false negative results. An IgM ELISA immunoassay (DCL-M) has been reported to be more sensitive and specific. A Western blot test for syphilis IgM antibody has been reported, with results also better than the FTA-IgM. However, more evaluations are needed for both the ELISA and Western blot.