Does Listeria Cause Birth Defects?

The direct answer is no: Listeria infection during pregnancy does not cause structural birth defects like spina bifida, heart malformations, or limb abnormalities. Research consistently shows no increase in congenital malformation rates above the baseline 3% to 5% that occurs in all pregnancies.

But this answer doesn’t capture the full danger of Listeria during pregnancy. While it doesn’t cause birth defects in the traditional sense, Listeria infection is devastating in other ways. It causes miscarriage, stillbirth, and premature birth at dramatically elevated rates. When infection occurs in the first trimester, fetal loss approaches 100%. In the second trimester, approximately 70% of pregnancies are lost. Babies who survive face severe infections including sepsis and meningitis that can cause permanent brain damage, seizures, blindness, and intellectual disability.

Understanding what Listeria does and doesn’t do helps pregnant women take appropriate precautions, recognize symptoms requiring urgent care, and understand what’s at stake. This article examines the medical evidence about Listeria and pregnancy, explains the distinction between birth defects and infection-related complications, and provides practical information about prevention and treatment.

What Listeria Monocytogenes Is and Why Pregnancy Makes Women Vulnerable

Listeria monocytogenes is a bacterium found in certain foods that causes a serious infection called listeriosis. While relatively rare in the general population, it poses unique dangers during pregnancy.

Where Listeria Lives and How People Get Infected

Listeria thrives in cold environments, unlike most bacteria that refrigeration inhibits. It’s found in:

• Soil and water
• Animal intestines and feces
• Unpasteurized dairy products
• Ready-to-eat deli meats and hot dogs
• Soft cheeses made from unpasteurized milk
• Smoked seafood
• Raw sprouts
• Melons and other produce contaminated through soil or processing

People become infected by eating contaminated food. The bacteria cross the intestinal lining, enter the bloodstream, and can spread throughout the body.

Why Pregnant Women Are 10 to 20 Times More Susceptible

Pregnancy creates unique vulnerability to Listeria through immune system changes that prevent rejection of the fetus. The same adaptations that allow the body to tolerate a genetically foreign fetus also reduce ability to fight certain infections.

Pregnant women are 10 to 20 times more likely than non-pregnant adults to contract listeriosis after exposure to contaminated food. This dramatically elevated susceptibility makes food safety precautions during pregnancy critical.

How Listeria Crosses the Placenta to Infect the Fetus

Once Listeria enters the maternal bloodstream, it can cross the placenta and directly infect the fetus. Few bacteria can accomplish this placental crossing, but Listeria has specific mechanisms enabling it to invade placental cells and reach fetal circulation.

This transplacental infection is what makes listeriosis so dangerous during pregnancy. The infection doesn’t just affect the mother. It directly attacks the developing baby.

The Timeline of Infection and Fetal Risk

Timing of infection dramatically affects outcomes:

When infection occurs in the first trimester, fetal loss approaches 100%. The developing embryo cannot survive the overwhelming bacterial infection. When infection occurs in the second trimester, approximately 70% of pregnancies end in miscarriage or stillbirth. In the third trimester, the fetus has better immune defenses but still faces high risks of premature birth and severe neonatal infection.

The earlier in pregnancy infection occurs, the worse the prognosis.

The Difference Between Birth Defects and Infection-Related Complications

Understanding terminology helps clarify what Listeria does and doesn’t cause.

What Birth Defects Actually Are

Birth defects, also called congenital anomalies or malformations, are structural problems present at birth. Common examples include:

• Neural tube defects like spina bifida
• Heart defects affecting cardiac structure
• Cleft lip or cleft palate
• Limb malformations
• Kidney or urinary tract abnormalities
• Chromosomal abnormalities like Down syndrome

These structural problems develop during fetal formation, typically in the first trimester when organs are forming. They result from genetic factors, environmental exposures during critical developmental windows, or combinations of both.

Why Listeria Doesn’t Cause Structural Malformations

Listeria is an infection, not a teratogen. Teratogens are substances that disrupt normal fetal development and cause malformations. Examples include certain medications, alcohol, and infections like rubella.

Listeria doesn’t interfere with the developmental processes that create structures and organs. It doesn’t cause cells to divide abnormally or organs to form incorrectly. Research consistently shows that among babies who survive maternal Listeria infection, rates of structural birth defects match the 3% to 5% baseline rate in the general population.

What Listeria Actually Causes Instead

Rather than causing malformations, Listeria causes:

• Direct bacterial infection of the fetus
• Overwhelming sepsis that the fetal immune system can’t fight
• Inflammation and tissue damage from infection
• Placental damage affecting oxygen and nutrient delivery
• Premature labor triggered by infection
• Stillbirth when infection is severe

These are fundamentally different from structural birth defects even though outcomes can be equally or more devastating.

Secondary Disabilities From Severe Neonatal Infection

When newborns survive Listeria infection, the infection itself can cause permanent damage:

• Bacterial meningitis damages brain tissue causing intellectual disability, cerebral palsy, seizures, and vision or hearing loss
• Septic shock affects multiple organs potentially causing lasting organ dysfunction
• Abscesses in organs can cause permanent scarring and functional impairment
• Prolonged oxygen deprivation during critical illness can cause brain injury

These are acquired injuries from infection, not congenital malformations present at birth. The distinction matters medically even though the outcomes affect the child lifelong.

The Devastating Pregnancy Outcomes Listeria Does Cause

While Listeria doesn’t cause birth defects, its actual effects on pregnancy are severe and often catastrophic.

Miscarriage and Stillbirth Rates

Listeria is one of the leading causes of infection-related pregnancy loss. Statistics are stark:

• First-trimester infection results in fetal loss approaching 100%
• Second-trimester infection causes loss in approximately 70% of cases
• Overall, about 1 in 4 pregnant women with listeriosis lose their pregnancy
• Stillbirth rates in Listeria-affected deliveries reach 13.5% compared to 0.7% baseline

These aren’t small increases. Listeria infection devastates pregnancy outcomes at rates far exceeding most other pregnancy complications.

The Mechanism of Fetal Death

Fetal death from Listeria results from:

• Overwhelming bacterial infection that fetal immune defenses cannot contain
• Placental inflammation and damage reducing oxygen and nutrient supply
• Maternal fever and inflammatory response affecting fetal wellbeing
• Direct bacterial damage to fetal organs and tissues

The infection is simply too severe for the developing fetus to survive, particularly in earlier pregnancy before the fetal immune system has developed.

Preterm Birth in Surviving Pregnancies

Among pregnancies that don’t end in loss, preterm birth is extremely common. Data shows:

• 61.3% of Listeria-affected deliveries are preterm compared to 7.7% baseline
• This nearly 8-fold increase makes preterm birth the norm rather than exception
• Many deliveries are emergency deliveries prompted by fetal distress or maternal illness

The infection triggers premature labor through inflammatory processes. Emergency delivery may be necessary to treat the infected baby with antibiotics.

Granulomatosis Infantiseptica

This severe form of neonatal Listeria infection involves widespread abscesses throughout the body:

• Small abscesses form in liver, spleen, lungs, kidneys, and other organs
• Characteristic rash of pustules appears on skin
• Mortality is very high even with treatment
• Survivors often have organ damage from widespread infection

This disseminated infection represents the most severe manifestation of congenital listeriosis.

Neonatal Listeriosis and Its Long-Term Consequences

Babies infected before or during birth face immediate life-threatening infection and potential long-term disabilities.

Early Onset vs Late Onset Neonatal Listeriosis

Neonatal Listeria infection occurs in two patterns:

Early-onset disease develops within the first few days of life, representing infection acquired before birth through placental transmission. This form causes sepsis and widespread infection often present at delivery. Late-onset disease develops after the first week of life, typically from exposure during delivery or postnatally. This form more commonly causes meningitis.

Both forms are serious, but early-onset disease with its association with prematurity and severe systemic infection generally has worse outcomes.

Meningitis and Brain Damage

Listeria has particular affinity for the central nervous system. Meningitis, inflammation of membranes surrounding the brain and spinal cord, occurs in approximately 60% to 70% of neonatal Listeria cases.

Bacterial meningitis in newborns causes:

• Direct bacterial damage to brain tissue
• Inflammation injuring neurons and brain structures
• Increased pressure and swelling affecting brain function
• Potential abscess formation in brain tissue

Even with prompt antibiotic treatment, neonatal bacterial meningitis carries high risk of permanent neurological damage.

Long-Term Disabilities in Survivors

Among infants who survive severe neonatal listeriosis, long-term complications can include:

• Intellectual disability ranging from mild to severe
• Cerebral palsy affecting movement and posture
• Seizure disorders requiring ongoing medication
• Vision loss from optic nerve damage or cortical blindness
• Hearing loss from auditory nerve damage or inner ear infection
• Hydrocephalus requiring surgical shunt placement
• Developmental delays across multiple domains

The severity of long-term effects generally correlates with severity of initial infection and how quickly treatment began. Early recognition and aggressive antibiotic treatment improves outcomes but doesn’t eliminate risk of permanent damage.

Mortality Rates in Infected Newborns

Despite modern antibiotics and neonatal intensive care, mortality from neonatal listeriosis remains approximately 20% to 30%. This reflects:

• Severity of infection in small, premature infants
• Difficulty treating overwhelming sepsis
• Multiple organ involvement
• Delays in diagnosis when symptoms are nonspecific

The babies who die and those who survive with severe disabilities together represent the tragic toll of maternal listeriosis.

How Listeria Infection Is Diagnosed and Treated During Pregnancy

Early recognition and treatment of maternal listeriosis can prevent or reduce fetal infection and improve outcomes.

Symptoms of Listeriosis in Pregnant Women

Maternal listeriosis causes symptoms that can be vague and easily mistaken for flu or normal pregnancy discomforts:

• Fever and chills
• Muscle aches
• Fatigue
• Nausea and diarrhea
• Headache
• Stiff neck if meningitis develops

Many pregnant women with Listeria have mild symptoms and don’t realize they’re seriously ill. This subtlety of symptoms contributes to delays in diagnosis and treatment.

When to Seek Medical Evaluation

Pregnant women should seek prompt medical evaluation for:

• Fever over 100.4°F
• Flu-like illness, particularly with muscle aches
• Symptoms after eating high-risk foods
• Any illness that seems more than a common cold
• Decreased fetal movement after mid-pregnancy

Early evaluation allows for blood cultures and prompt antibiotic treatment if Listeria is suspected or confirmed.

Diagnostic Testing for Listeria

Diagnosis requires blood culture growing Listeria monocytogenes. This involves:

• Drawing blood and culturing it for bacterial growth
• Waiting 24 to 48 hours for culture results
• Sometimes starting empiric antibiotics before confirmation if suspicion is high
• Additional cultures from other sites if disseminated infection is suspected

The challenge is that many pregnant women with compatible symptoms don’t have Listeria, making it difficult to know when to culture versus treating symptomatically.

Antibiotic Treatment for Maternal and Fetal Infection

When Listeria is confirmed or strongly suspected, immediate antibiotic treatment is critical:

• Ampicillin is the primary treatment, often combined with gentamicin
• Treatment duration is typically 2 to 4 weeks for maternal bacteremia
• Earlier treatment in pregnancy improves outcomes
• Antibiotics cross the placenta and treat fetal infection
• Treatment doesn’t guarantee fetal survival but substantially improves chances

Prompt treatment can prevent stillbirth and reduce severity of neonatal infection, making rapid diagnosis and immediate antibiotics lifesaving.

Preventing Listeria Infection Through Food Safety

Since Listeria infection is foodborne, prevention centers on avoiding contaminated foods and practicing safe food handling.

High-Risk Foods Pregnant Women Should Avoid

Specific foods carry highest Listeria risk:

• Unpasteurized milk and products made from it
• Soft cheeses like feta, brie, camembert, blue cheese, and queso fresco unless clearly labeled as made from pasteurized milk
• Deli meats and hot dogs unless heated to steaming before eating
• Refrigerated pâté and meat spreads
• Smoked seafood unless cooked in a dish
• Raw sprouts of any kind
• Unwashed produce
• Melons with contaminated rinds

Complete avoidance of these foods eliminates most Listeria risk from diet.

Safe Food Handling and Preparation Practices

Additional precautions reduce risk:

• Cook meat, poultry, and seafood to safe internal temperatures
• Wash all fruits and vegetables thoroughly before eating
• Keep refrigerator at 40°F or below
• Clean up spills in refrigerator promptly
• Separate raw meats from ready-to-eat foods
• Wash hands, utensils, and surfaces after contact with raw foods
• Reheat leftover foods to steaming before eating
• Consume perishable foods within recommended timeframes

These practices reduce risk but don’t eliminate it entirely since Listeria can contaminate even properly handled foods during processing or packaging.

Reading Labels and Making Safe Choices

When shopping:

• Choose pasteurized dairy products
• Check labels on cheese confirming pasteurization
• Select prepackaged deli meats over freshly sliced
• Buy pre-washed produce but wash again at home
• Check expiration dates and don’t consume expired foods
• Be aware of recalls and avoid implicated products

Staying informed about food recalls helps avoid contaminated products.

Special Precautions When Eating Out

Restaurant meals pose additional challenges:

• Ask about cheese types in dishes
• Ensure deli sandwiches are made with heated meats
• Avoid salad bars where cross-contamination can occur
• Choose cooked menu items over raw or cold options
• Skip soft-serve ice cream machines that may not be properly cleaned

While being vigilant, remember that absolute risk from any single exposure remains low. These precautions reduce already-small baseline risk further.

What to Do If You’ve Been Exposed to Listeria During Pregnancy

Despite precautions, exposure sometimes occurs. Knowing how to respond reduces risk of serious infection.

If You’ve Eaten Recalled Food

When learning you consumed a product later recalled for Listeria:

• Monitor for symptoms over the next 2 to 8 weeks (Listeria has long incubation)
• Report any fever, flu-like illness, or decreased fetal movement immediately
• Inform your healthcare provider about the exposure
• Don’t panic, as most exposures don’t result in infection
• Follow your provider’s guidance about whether testing or empiric treatment is warranted

Most people exposed to Listeria-contaminated food don’t develop infection, but vigilance is important.

Symptoms Requiring Immediate Medical Attention

Seek urgent evaluation for:

• Fever during pregnancy
• Flu-like illness with muscle aches and headache
• Decreased fetal movement after mid-pregnancy
• Symptoms following known or suspected exposure

Prompt evaluation allows for blood cultures and immediate treatment if indicated.

Testing and Monitoring Options

Your healthcare provider might recommend:

• Blood cultures if symptoms develop
• Fetal monitoring to assess baby’s wellbeing
• Sometimes empiric antibiotic treatment while awaiting culture results
• Ultrasound to check fetal growth and amniotic fluid
• Follow-up monitoring if exposure was recent but symptoms haven’t developed

The approach depends on timing of exposure, presence of symptoms, and individual risk factors.

The Reality of Listeria Risk in Perspective

While the consequences of listeriosis are severe, understanding actual risk helps maintain reasonable vigilance without excessive anxiety.

How Common Listeriosis Is During Pregnancy

Listeriosis is rare:

• Approximately 1,600 to 1,700 cases occur annually in the United States
• About 17% of cases occur in pregnant women
• This represents roughly 270 to 290 cases in pregnant women per year
• Given approximately 3.7 million births annually, the rate is about 1 in 13,000 to 14,000 pregnancies

The absolute risk of contracting listeriosis during pregnancy is very low.

Why Food Safety Precautions Still Matter

Despite low absolute risk:

• Consequences when infection occurs are catastrophic
• Prevention through diet modification is relatively simple
• No way to predict who will be the unlucky few who contract infection
• Avoiding high-risk foods has minimal impact on nutrition or quality of life

The severity of outcomes justifies precautions even for a rare infection.

Balancing Caution With Reasonable Living

Food safety guidance shouldn’t create paralyzing anxiety:

• Perfect adherence isn’t necessary or realistic
• Occasional lapses don’t mean disaster
• Stress about diet is counterproductive
• Most women who avoid high-risk foods do so without difficulty

Reasonable precautions provide significant risk reduction without dominating pregnancy experience.

Moving Forward With Knowledge and Appropriate Precautions

Listeria infection during pregnancy does not cause structural birth defects, with rates of congenital malformations remaining at the baseline 3% to 5% seen in all pregnancies. However, this reassuring fact about birth defects doesn’t diminish the serious dangers Listeria does pose through infection-related complications including miscarriage approaching 100% in first-trimester infections, stillbirth rates of 13.5% compared to 0.7% baseline, preterm birth affecting 61.3% of surviving pregnancies versus 7.7% normally, and severe neonatal sepsis and meningitis in approximately two-thirds of exposed newborns.

Survivors of severe neonatal listeriosis face risk of permanent disabilities including intellectual disability, cerebral palsy, seizure disorders, and vision or hearing loss resulting from bacterial meningitis and overwhelming infection rather than from congenital malformations. The distinction between birth defects and infection-acquired disabilities matters medically but provides little comfort to families facing devastating outcomes from this preventable foodborne infection.

Prevention through avoiding high-risk foods including unpasteurized dairy products, deli meats, soft cheeses, and smoked seafood, combined with prompt medical attention for any fever or flu-like illness during pregnancy, provides the best protection against listeriosis and its catastrophic consequences. While the absolute risk of contracting Listeria remains low at approximately 1 in 13,000 to 14,000 pregnancies, the severity of outcomes when infection occurs fully justifies the relatively simple dietary precautions that dramatically reduce exposure risk.