Pregnancy and Lyme Disease: Why Scientists Say More Research Is Needed

Lyme disease is already the most common vector-borne illness in the United States, with the Centers for Disease Control and Prevention (CDC) estimating approximately 476,000 new diagnoses each year. Yet despite decades of research into the tick-borne infection, one area remains surprisingly understudied: whether Lyme disease can be transmitted from mother to child during pregnancy and around the time of birth.

A recent scientific review is drawing attention to that knowledge gap. The paper, co-authored by Charlotte Mao, M.D., infectious disease pediatrician with the Bay Area Lyme Foundation, examines decades of published evidence and calls for more comprehensive research into the potential risks of Lyme disease during pregnancy.

Perinatal transmission refers to the transfer of an infection from mother to baby before birth, during delivery or shortly after birth. In the case of Lyme disease, investigators are examining whether the bacteria responsible for the illness, Borrelia burgdorferi, can cross the placenta during pregnancy, be transmitted during the birth process or potentially be passed after delivery.

According to Mao, evidence suggesting that mother-to-child transmission can occur has existed since the mid-1980s. The first documented case was reported in 1985, and additional case reports and case series have been published over the decades since. However, researchers say the topic has never received the level of scientific attention necessary to answer key questions about frequency, diagnosis, risk factors and outcomes.

One challenge is that many of the earlier studies lacked the sophisticated testing methods available today. Investigators often relied primarily on blood antibody testing, which may not be sufficient to determine whether a baby acquired Lyme disease before birth. More comprehensive approaches involving placental tissue, additional body fluids and long-term follow-up have rarely been performed.

As a result, Mao explained, experts still do not know how frequently perinatal Lyme transmission occurs. They also do not know which pregnant women may be at greatest risk or what the full spectrum of potential effects on infants and children might be. Experts generally believe that treatment can and does reduce transmission risk, but what is not established is the best regimen to use in pregnancy to reduce that risk as much as possible.

These questions are especially important because Lyme disease may not always be easy to recognize during pregnancy. Some evidence suggests pregnant women may be less likely to develop classic symptoms such as the characteristic erythema migrans rash or flu-like illness. If infections go unrecognized, opportunities for diagnosis and treatment could be missed.

Mao and her team are also interested in understanding whether effects of congenital Lyme infection, if they occur, might appear later in childhood rather than immediately after birth. Other congenital infections, including syphilis and Chagas disease, can sometimes remain undetected for years before symptoms emerge, highlighting the importance of long-term study.

Mao noted that many infectious diseases with far fewer annual cases have established guidance for managing pregnancy-related transmission risks. By comparison, Lyme disease lacks comprehensive, up-to-date consensus guidelines specifically addressing pregnancy and newborn care.

For patients, the review is not intended to cause alarm. Rather, its purpose is to encourage awareness and support further scientific investigation. Mao emphasized that many questions remain unanswered and that well-designed studies are needed before definitive conclusions can be reached. She calls for larger, federally funded research efforts that follow pregnant women and their children over time. Such studies could help determine how often transmission occurs, identify the most effective diagnostic tests and clarify whether specific interventions can reduce risks to mothers and babies.

In the meantime, Mao says it’s important for health care professionals and the public to recognize that Lyme disease during pregnancy remains an area requiring greater attention. Increased awareness, improved education and additional research may ultimately help provide clearer answers for families and clinicians navigating Lyme disease during one of life's most important stages.