Current research into the effects of untreated Lyme disease during pregnancy appears to show that complications are relatively rare although there is clearly some degree of risk to both mother and foetus in any infection. In cases where the infection was present prior to conception the risk of stillbirth or gestational abnormality does not appear to be increased, whereas infection which is acquired during the pregnancy does seem to increase such risks.There are a handful of studies suggesting that Borrelia burgdorferi may be transmitted via the placenta to a developing foetus, with the risk higher during the first trimester. Much of this evidence comes from animal studies however, which affects its applicability to human patients. No severe effects have been noted in the offspring of those women infected with Lyme prior to pregnancy. Untreated Lyme disease does not appear to be contagious between a human mother and breastfeeding infant, despite some animal studies (on mice) showing that the infection can be transmitted in this fashion. This goes some way to demonstrating the problems inherent in applying animal experimentation results to a human population.
Foetal Death in Mice with Lyme Disease
Silver, et al (1995), studied the effects of acute infection with Borrelia burgdorferi in mice during early pregnancy and observed foetal death in 12% of sacs of those mice infected four days after mating compared to control mice who suffered no such foetal deaths. Mice infected with the Lyme disease bacteria had a 46% incidence of at least one foetal death. Mice infected three weeks prior to mating however had no foetal deaths and there was no evidence in the uteri of these chronically infected mice of Borrelia burgdorferi DNA. Acutely infected mice did have evidence of Borrelia burgdorferi DNA in their uteri but the bacterial DNA was found only rarely in foetal tissue samples and was not correlated with foetal death. The researchers concluded that it was the maternal response to infection during pregnancy that contributed to foetal death rather than the infection of the foetus itself. It is extremely important, therefore, to determine the factors leading to foetal death in order to appropriately, and promptly, treat patients who become infected with Lyme disease whilst pregnant.
Can Research in Mice Translate to Humans?Studies in murine models (mice) do not necessarily translate to human patients however, especially given the nature of pregnancy in mice with multiple sacs and infants. Lakos (et al, 2010) performed a review of the data collected over twenty-two years from 95 women with Lyme disease during pregnancy. These patients, evaluated at the Center for Tick-borne Diseases in Budapest, were treated for Lyme disease in nearly 90% of cases, most parenterally and the rest with oral antibiotics. Those with untreated Lyme disease had adverse pregnancy outcomes in 60% of cases, compared to 12.1% in those women treated parenterally and 31.6% of those treated orally.
Higher Risk in Pregnancy With Unsuccessful Lyme Treatment
Patients who were treated did not always have resolution of erythema migrans with a single course of antibiotics and those patients requiring further treatment had a higher risk of complications compared to those successfully treated with a single course of antibiotics. The difference was not statistically significant however and may have been due to simple chance. The most common adverse outcomes included in the study were loss of pregnancy, which occurred in seven cases, and cavernous hemangioma (four cases) which is a rare condition involving abnormal blood vessel formation. The research shows evidence that adverse outcome does occur in cases of Lyme disease in pregnancy but does not shed any further light on the pathology involved nor the relative risks in regards to the timing of the infection (i.e. prenatal or pre-conception).
Up to a Quarter of Stillbirths May be Due to Infection
Research by McClure, et al (2009), does however have some bearing on the possible pathology at work in adverse outcomes such as stillbirth in pregnant women who contract Lyme disease. These researchers propose that direct infection of the foetus, damage to the placenta, and severe maternal illness are mechanisms contributing to foetal death. McClure estimates that between 10% and 25% of stillbirths in developed countries may be attributed to infection, and that such deaths are likely higher in developing countries. The most common infections leading to stillbirth include syphilis (a spirochaetal infection like Borrelia burgdorferi), Escherichia coli, group B streptococci, and Ureaplasma urealyticum. Malaria is also indicated in many stillbirths.
Antibiotic Treatment in Pregnancy
Due to the potential for complications in untreated Lyme disease in pregnancy, some have suggested that prophylactic antibiotic administration is a good idea for women in Lyme-endemic areas. Most researchers appear to support the ‘watch and wait’ approach however, given that the possible side-effects of antibiotics outweigh the likelihood of becoming infected with Lyme disease and remaining untreated for any length of time (Maraspin, et al, 2009).
The use of appropriate antibiotics to treat Lyme disease during pregnancy should reduce the risk of adverse outcome to very low levels but women should be aware of the importance of restoring good bacteria to their systems following such treatment. Dysbiosis in pregnancy, which can result from antibiotic treatment, can allow other infections to take hold which could be detrimental to both mother and child. Careful management of the condition is clearly needed in such cases but there is no rationale for allowing untreated Lyme disease to remain untreated given the availability of antibiotics safe for use in pregnancy.
McClure EM, Goldenberg RL., Infection and stillbirth. Semin Fetal Neonatal Med. 2009 Aug;14(4):182-9. Epub 2009 Mar 12.
Maraspin V, Strle F., How do I manage tick bites and Lyme borreliosis in pregnant women? Curr Probl Dermatol. 2009;37:183-90. Epub 2009 Apr 8.
Elliott DJ, Eppes SC, Klein JD., Teratogen update: Lyme disease. Teratology. 2001 Nov;64(5):276-81.
Lakos A, Solymosi N., Maternal Lyme borreliosis and pregnancy outcome. Int J Infect Dis. 2010 Jun;14(6):e494-8. Epub 2009 Nov 18.
Silver RM, Yang L, Daynes RA, Branch DW, Salafia CM, Weis JJ., Fetal outcome in murine Lyme disease. Infect Immun. 1995 Jan;63(1):66-72.