Diagnostic considerations in intra-amniotic syphilis

Amniotic fluid is rarely used in the evaluation of syphilis during pregnancy but was available from a woman with positive serologic tests in the 30th week of gestation. Nonmotile intra-amniotic spirochetes were seen by dark-field microscopy 20 hr after treatment with benzathine penicillin G. The identity of the organism in amniotic fluid was confirmed by immunofluorescent staining. Less than 0.5 units/ml of penicillin was present in the amniotic fluid at this time. The amniotic fluid was positive in the Venereal Disease Research Laboratory (VDRL; Atlanta, GA) test, and the concentration of IgM was elevated as was the ratio of lecithin to sphyngomyelin. Phosphatidyl inositol and phosphatidyl glycerol were also present in the amniotic fluid. After treatment the lecithin-sphyngomyelin ratio declined; phosphatidyl glycerol disappeared, whereas phosphatidyl inositol was still present. Despite evidence of intrauterine growth retardation at 30 weeks, the infant born at 37 weeks was of normal weight and length; however, the head circumference was below the tenth percentile. These studies suggest that analysis of amniotic fluid may provide new insights into the biology of syphilis in pregnancy, but does not constitute a recommendation for routine examination of the amniotic fluid in mothers with reactive serologic tests for syphilis.