One of the authors (AL) presented a poster on 34 pregnancies of maternal Lyme borreliosis (Lb) in 1995. It was striking that untreated Lb associated with higher probability of adverse outcome but the number of patients were small and the statistical power was low. We have recently published a paper on 95 maternal Lb and the outcome of their pregnancies. Since the closure of the database for that manuscript the number of the pregnant women with Borrelia infection observed in our Centre increased to 124, and the statistical analysis strengthened our previous doubtful observations and reached significant results in important aspects by now. This series is the largest study to date on this topic. Treatment was administered parenterally to 87 (70%) women and orally to 25 (20.0%). Infection remained untreated in 12 (10%) pregnancies. Adverse outcomes were seen in 7/87 (8%), 9/25 (36%), 8/12 (67%), of the parenterally, orally treated and untreated women, respectively. In comparison to patients treated with antibiotics, untreated women had a significantly higher risk of adverse pregnancy outcomes (OR: 11.62, p<0.001). Mothers treated orally comparing to iv. treatment had an increased chance (OR: 6.28) to have an adverse outcome (p=0.001). In the adverse pregnancy outcome, the most impressive difference was between the untreated and parenterally treated women (OR: 21.44, p<0.001). The probability of adverse outcome increased by the exposition time (from the first maternal symptom to the treatment or delivery). When the exposition time has reached four months, the probability of adverse outcome increased by 33%. We had no chance to examine the bacterial invasion of the foetus. Loss of the pregnancy (N=9), small for gestational age or preterm birth (N=7) were the most prevalent adverse outcomes in our series. The other complications were heterogeneous. Our results indicate that untreated or orally treated maternal Borrelia burgdorferi s.l. infection is associated with adverse outcomes. 'Congenital Lyme disease' similar to the Hutchinson's triad in syphilis is unlikely.

