Lyme disease is caused by the bacterium Borrelia burgdorferi, primarily transmitted through the bite of an infected blacklegged tick. If left untreated, this spirochete infection can affect multiple body systems. When Lyme disease occurs during pregnancy, the potential for the bacteria to pass from the mother to her developing child is a serious concern. Understanding the risk of this transfer and its consequences is crucial for pregnant individuals in endemic areas.
The Scientific Consensus on Vertical Transmission
The medical community holds that the transmission of Borrelia burgdorferi from a pregnant woman to her fetus, known as vertical or transplacental transmission, is possible but rare. This possibility exists because the bacteria have been documented to cross the placenta, the organ responsible for nutrient and waste exchange. Case studies have provided evidence of the bacteria in placental tissue and, in rare instances, in fetal tissue following an adverse outcome.
The spirochete’s motility is thought to aid its ability to penetrate and infect various tissues, including the placenta. Official health guidance emphasizes that transmission is uncommon, especially when the maternal infection is treated promptly. Although direct evidence of transmission is difficult to confirm definitively in human studies, the biological plausibility is recognized. This leads to the recommendation that all pregnant women with confirmed or suspected Lyme disease receive immediate treatment.
Potential Fetal and Neonatal Outcomes
When maternal Lyme disease is not identified and treated with appropriate antibiotics, adverse outcomes for the fetus and newborn can occur. Untreated infection has been associated with complications such as spontaneous abortion, stillbirth, and premature delivery. Other reported issues include intrauterine growth restriction, resulting in a low birth weight.
The most severe consequences, including fetal demise, are linked to infections that go untreated or are diagnosed in the late stages of pregnancy. If an infant is born with an infection, symptoms are often non-specific, which can complicate initial recognition. These signs may include respiratory distress, hyperbilirubinemia (jaundice), hypotonia (poor muscle tone), and, in rare cases, cardiovascular or neurological abnormalities.
Challenges in Diagnosis and Testing
Diagnosing Lyme disease in a pregnant woman is complicated because the initial symptoms can mimic common discomforts of pregnancy, such as fatigue and body aches. Standard serologic tests, which detect antibodies using ELISA followed by a Western Blot, are not highly sensitive in the early stages of infection. In the first few weeks after exposure, these tests may produce a false negative result before the body mounts a sufficient antibody response.
Diagnosing the infection in a newborn presents challenges related to the transfer of maternal antibodies. A positive Immunoglobulin G (IgG) antibody test often reflects the mother’s past or current infection, as these antibodies cross the placenta to provide passive immunity. This positive result does not necessarily mean the baby is actively infected, making serology unreliable in the first months of life. Specialized techniques like Polymerase Chain Reaction (PCR) testing on fetal or placental tissue are sometimes used to directly detect the bacterial DNA, though this is not a routine procedure.
Managing Lyme Disease During Pregnancy
Immediate antibiotic treatment is the most important factor in reducing the risk of adverse outcomes associated with Lyme disease during pregnancy. Treatment protocols for pregnant individuals differ from those for the general population due to concerns about fetal safety. Oral antibiotics such as amoxicillin or cefuroxime axetil are the preferred first-line treatments for early-stage disease, typically prescribed for a two- to three-week course.
If the infection is severe or has spread to the central nervous system or heart, intravenous treatment with Ceftriaxone may be administered. Doxycycline, a common and effective Lyme treatment, is generally avoided in the second and third trimesters of pregnancy. This tetracycline-class antibiotic carries a risk of causing cosmetic staining of the primary dentition and potential effects on fetal bone development. Successfully treating the mother’s infection significantly lowers the already small risk of the bacteria affecting the fetus.