Viral and Bacterial Infections and Pregnancy Loss

Although it can be difficult to pinpoint exactly what causes pregnancy loss, there are some infections that are associated with an increased risk of miscarriage, stillbirth, or neonatal death. It's important to take precautions to lower your risk of contracting an infection during pregnancy, but it's equally important to note that most pregnant people who get an infection will not experience a pregnancy loss, especially if they receive timely and appropriate medical care.

The most common cause of pregnancy loss is chromosomal abnormalities, an issue over which parents have no control. The following list does not cover every possible infection that can occur during pregnancy, but it touches on some of the most common that pregnant people may have concerns about.

Bacterial Vaginosis (BV)

Bacterial vaginosis (BV) is the excess growth and imbalance of normal vaginal bacteria, including ureaplasma and mycoplasma. Symptoms can be mild, and BV often does not require treatment in non-pregnant women. But when you're pregnant, it's important to consult your doctor at the first sign of this infection.

BV is not a sexually transmitted infection (STI), but as it is a vaginal infection, many women will notice its characteristic "fishy" odor, particularly after intercourse. Though a common symptom, sometimes there is no noticeable odor or any other signs or symptoms. But some women will experience vaginal itching, a white or gray discharge, and/or burning during urination.

In pregnancy, BV has been associated with an increased risk of second-trimester miscarriage. Later in pregnancy, BV may cause uncomfortable uterine contractions. But the condition is easily treated with an antibiotic, and once treated, has no lasting health effects for parent or baby.


Brucellosis is an infectious disease caused by bacteria from infected animals or contaminated animal products such as unpasteurized dairy products. Symptoms are usually mild and include fever, headache, and fatigue.

This is a rare infection and it can be treated with antibiotics. But research has shown that it can pose a risk of miscarriage in pregnant people who become infected and do not receive prompt treatment.

Chickenpox (Varicella)

Although most adults are immune to chickenpox (through vaccination or previously having the disease), a limited number of pregnant people are not immune and can contract the virus. Symptoms typically include an itchy rash, fever, fatigue, and headache.

The risk in pregnancy depends on how far along you are when you are exposed to chickenpox. There is little risk in the first trimester, and up to 36 weeks gestation, the risk to the fetus is small. The risk is greatest when a pregnant person contracts varicella within a few days of delivery. This timing can lead to neonatal varicella, which carries some risk of death for newborns, especially if they're premature.


Chlamydia is one of the most common sexually transmitted infections. If left untreated, it can lead to pelvic inflammatory disease (PID), which is a known cause of ectopic pregnancy and infertility. Ectopic pregnancy is an obstetric emergency and requires surgery to prevent serious complications, including a risk of death.

Some research published in 2011 suggests chlamydia also may contribute to miscarriage in the first trimester. Chlamydia is routinely screened for early in pregnancy so it can be treated if detected. Symptoms include vaginal discharge and painful urination. Like all bacterial infections, chlamydia is treated with antibiotics. Condoms can protect you against chlamydia.

Cold and Flu

Although there is no known risk of miscarriage with a viral cold or flu (influenza) during pregnancy, high fever has been linked to neural tube defects in infants. Although there is no cure for these viral infections, the chance of getting one can be reduced through good hygiene practices, like hand-washing and avoiding others who have active colds or flu.

The flu vaccine is recommended for pregnant people to reduce the risk of potential complications from flu infection. Ideally, seasonal influenza vaccination should be given in early fall (by the end of October). However, the vaccination is still useful any time during the season and can be given in any trimester.


Research is ongoing to fully understand how COVID-19 affects fetuses, but early findings show a slightly higher risk for problems when pregnant people have the virus. A multi-center study found that COVID-19 is associated with a higher rate of various pregnancy complications and pre-term birth.

Reduce your risk of contracting COVID-19 by getting vaccinated and limiting your interactions with people who are sick. Symptoms of COVID-19 include fever, loss of smell, and fatigue. Talk with your healthcare provider about any concerns you have about COVID-19.


Cytomegalovirus (CMV) is a common infection with easily dismissed symptoms, like mild fever, swollen glands, and flu-like symptoms. Healthy adults rarely have any serious health effects with a CMV infection.

In pregnancy, however, exposure to CMV can lead to an infant born with the infection, resulting in a risk of serious, lifetime complications such as microcephaly, developmental delays, or vision and hearing problems. The infection can also be fatal.

Dengue Fever

Though it's rare in the United States, dengue fever is the most common mosquito-borne infection worldwide. While researchers say its relationship to miscarriage is unknown, transmission to fetuses and pregnancy loss after infection have been reported.

While there is no specific treatment available to treat dengue fever, symptoms are usually mild and include fever, aches and pains, or a rash. The infection usually clears within two to seven days.

Escherichia Coli (E. Coli)

Although Escherichia coli (E. coli) bacteria live in everyone’s intestinal tracts, if you have an active infection, some forms of it have been associated with a risk of miscarriage. There is no specific food source associated with E. coli, but it can be found in any unsanitary or undercooked food, contaminated water, or unwashed hands.

The best way to avoid E. coli is to follow proper food-handling techniques and to wash your hands frequently, especially after using the restroom and before eating or touching your mouth.


Although there is no conclusive evidence that gonorrhea causes pregnancy loss, several studies have linked the sexually transmitted infection with miscarriage, preterm labor, and ectopic pregnancy (if it goes untreated long enough to cause PID). Symptoms include vaginal discharge and pain with urination.

Gonorrheal infection during birth can also cause life-threatening health problems for a baby. You can protect yourself against gonorrhea by using condoms during intercourse. If you already have it, gonorrhea can be treated with antibiotics.


There are many forms of hepatitis, but only one, hepatitis E, is associated with a risk of death for both parent and baby. Hepatitis E is extremely rare in the United States.

If a person becomes infected with viral hepatitis for the first time while in their third trimester of pregnancy, they are at risk for preterm labor or delivery. Some forms of hepatitis can also be passed on to a developing fetus and can cause long-term health complications.


Herpes (HSV) is a common sexually transmitted infection. It can cause painful sores on the genitals or mouth. A 2016 review study that found a link between miscarriage and herpes infections is controversial, as other research does not support this association. So, at this time, it's not believed that there is an increased risk of pregnancy loss with HSV.

However, there is a risk of the baby contracting HSV during birth if the gestational parent has an active infection, so medication may be given in the weeks leading up to birth to prevent transmission. If a person has active herpes lesions at the time of labor, physicians recommend a c-section for delivery.

Human Immunodeficiency Virus (HIV)

In the past, human immunodeficiency virus (HIV) infection was thought to dramatically increase the risk of miscarriage. Since the emergence of routine testing of pregnant people and more effective drug treatment, HIV-positive people can usually have healthy, full-term babies.

Initial HIV infections cause flu-like symptoms, followed by an asymptomatic period until the disease progresses to acquired immunodeficiency syndrome (AIDS), a disease characterized by recurrent infections, weight loss, fever, and fatigue. Medications can stop the infection from progressing to AIDS.

While there is no cure for HIV, there are excellent treatments available to control the virus. The spread of HIV can be prevented through condom use and other safe-sex techniques.


Listeria is a bacteria found in certain kinds of foods. It is most commonly associated with unpasteurized cheeses and deli meats, although it can also be found in fresh produce (for example, an outbreak of listeriosis in 2011 was traced back to cantaloupe). Listeriosis—infection due to listeria exposure—is one of four types of food poisoning that has a known risk of miscarriage.

While listeriosis is rare, it is 20 times more likely in pregnant people. Even then, the infection is not common. However, as it can result in serious complications for the fetus, it's recommended to take precautions. This is particularly important for Hispanic women who have a higher than average incidence of the infection.

Symptoms include fever, muscle aches, headache, vomiting, and loss of balance. Listeria is avoidable while pregnant through proper food handling, good hand-washing, and avoiding foods known to carry a higher risk of listeria infection:

  • Hot dogs, lunch meats, cold cuts (when served chilled or at room temperature; they are safe when heated to an internal temperature of 74°C [165°F] or steaming hot)
  • Raw (unpasteurized) milk
  • Refrigerated pâté and meat spreads
  • Refrigerated smoked seafood
  • Unpasteurized soft cheeses such as feta, queso blanco, queso fresco, Brie, queso panela, Camembert, and blue-veined cheeses
  • Unwashed raw produce such as fruits and vegetables (when eating raw fruits and vegetables, the skin should be washed thoroughly in running tap water, even if it will be peeled or cut)

Lyme Disease

Lyme disease is a bacterial infection spread by ticks. Symptoms are somewhat vague and mimic many common viral illnesses. But the area where the tick has bitten usually has a characteristic bulls-eye pattern around the bite, which often helps doctors identify potential Lyme disease cases.

Lyme disease has many long-term health effects if it is not diagnosed and treated early, but there is no conclusive evidence that pregnant people have an increased risk of pregnancy loss due to Lyme disease if they are being treated with antibiotics.


Like dengue, malaria is another infectious disease transmitted by bites from infected mosquitoes. Symptoms usually include fever, chills, headaches, nausea, vomiting, and body aches, and treatment usually depends on the severity of the illness, though it often involves antiparasitic drugs.

According to the Centers for Disease Control and Prevention (CDC), pregnant people are three times more likely to develop severe infections from malaria. Potential complications include premature birth, low birth weight, and miscarriage.

In addition to taking precautions to avoid mosquito bites, health officials recommend avoiding travel to areas with known malaria risk. If travel is unavoidable, there are antimalarial drugs available for prevention.


A common childhood illness, also known as fifth disease, parvovirus is not concerning for most healthy adults. Pregnant people exposed to parvovirus usually have a mild course of the illness. Less than 5% of pregnant people will have any complications after being exposed to parvovirus, but there is a risk of miscarriage associated with infection.


Commonly known as German measles, rubella is a generally mild infection that people recover from with no long-term effects. It is covered by the MMR vaccine, and a pregnant person's immunity is usually tested at the first prenatal visit. If, however, a person contracts rubella during pregnancy, there is a high risk of congenital birth defects, miscarriage, or stillbirth.


Salmonella is a bacteria that can cause infections in humans. It is commonly found in raw or undercooked animal sources like chicken, eggs, and unpasteurized dairy products. It may also be carried by reptiles, including household pets like turtles, snakes, and lizards. Salmonella has been associated with an increased risk of miscarriage.

Symptoms include diarrhea, vomiting, stomach cramps, and fever. Infection can be avoided through good food-handling techniques and thorough hand-washing.


Syphilis is a sexually transmitted infection that can be easily treated with antibiotics. Symptoms include painless genital sores, a rash, fever, fatigue, flu-like symptoms, and hair loss, as well as asymptomatic periods—which mean this STI can easily go undetected. Because it is one of the most dangerous STIs to have during pregnancy, women are routinely screened for it during regular prenatal care.

Untreated, syphilis can lead to stillbirth or neonatal death for up to 40% of infected women. There is also a risk of the baby developing congenital syphilis, which can cause long-term life-threatening or disabling complications.


Toxoplasmosis is another infection with a known risk of miscarriage. It is commonly associated with being exposed to cat feces, which can contain the parasite that causes the infection.

As a result, many obstetricians recommend that pregnant people avoid cleaning litter boxes during pregnancy. Often, people who have toxoplasmosis don't exhibit any symptoms, but if they do, they may have flu-like symptoms.

Toxoplasmosis can also be contracted by eating undercooked meat, but good food-handling techniques can eliminate the risk of contracting a food-borne illness.

Zika Virus

Zika virus is an infection spread by mosquitoes that tends to show mild symptoms. However, when contracted during pregnancy, it is known to cause microcephaly, a serious birth defect in which a baby's head is smaller than expected. This complication is why health officials recommend pregnant women not travel to areas where the virus is common (among other Zika-related precautions).

Recent research has shown that infection may be tied to miscarriage risk as well. However, because published research has only looked at animals and not humans, further investigation is needed to determine the true risk of miscarriage. There is no specific treatment for Zika. Instead, health officials advise infected patients to treat their symptoms and get plenty of rest while avoiding exposing others to the disease.

A Word From Verywell

It's important to be aware of viral and bacterial infections that can potentially cause miscarriage or other pregnancy complications. However, know that the likelihood of one of these infections causing a complication in your pregnancy is low—and if an issue does arise, prompt treatment will usually protect you and your baby.

The possibility of contracting an infection is one reason why prenatal care and routine screenings are so important to your health and the health of your baby. Talk to your doctor if you have any concerns or are experiencing any unusual symptoms.

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By Elizabeth Czukas, RN, MSN
Elizabeth Czukas is a writer who who has worked as an RN in high-risk obstetrics, antepartum care, and with women undergoing pregnancy loss.