Maternal Lyme disease and congenital malformations: a cord blood serosurvey in endemic and control areas.

This report describes a cohort study of over 5000 infants and their mothers who participated in a cord blood serosurvey designed to examine the relationship between maternal exposure to Lyme disease and adverse pregnancy outcome. Based on serology and reported clinical history, mothers of infants in an endemic hospital cohort are 5 to 20 times more likely to have been exposed to B. burgdorferi as compared with mothers of infants in a control hospital cohort. The incidence of total congenital malformations was not significantly different in the endemic cohort compared with the control cohort, but the rate of cardiac malformations was significantly higher in the endemic cohort [odds ratio (OR) 2.40; 95% confidence interval (CI) 1.25, 4.59] and the frequencies of certain minor malformations (haemangiomas, polydactyly, and hydrocele), were significantly increased in the control group. Demographic variations could only account for differences in the frequency of polydactyly. Within the endemic cohort, there were no differences in the rate of major or minor malformations or mean birthweight by category of possible maternal exposure to Lyme disease or cord blood serology. The disparity between observations at the population and individual levels requires further investigation. The absence of association at the individual level in the endemic area could be because of the small number of women who were actually exposed either in terms of serology or clinical history. The reason for the findings at the population level is not known but could be because of artifact or population differences.