Viral and Bacterial Infections and Pregnancy Loss

The Connection Between Infection, Miscarriage, and Pregnancy Complications

Although it is difficult to pinpoint what causes a pregnancy loss, there are some infections that are associated with an increased risk of miscarriage, stillbirth, or neonatal death. While it's important to take precautions to lower your risk of contracting an infection during pregnancy, it's also important to note that not every pregnant woman who gets an infection associated with pregnancy complications will experience a pregnancy loss. In fact, the most common cause of pregnancy loss remains chromosomal abnormalities, over which you 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 and the ones women often have concerns about.

Pregnant woman looking out a window
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Bacterial Vaginosis

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

BV is not a sexually transmitted infection, but as a vaginal infection, many women notice the characteristic “fishy” odor of BV after intercourse. Though a common symptom, sometimes there is no noticeable odor.

In pregnancy, BV has been associated with an increased risk of second-trimester miscarriage. Later in pregnancy, BV may cause uncomfortable uterine contractions. It is easily treated with an antibiotic and has no lasting health effects.


Chlamydia is a sexually transmitted infection and, if left untreated, can lead to pelvic inflammatory disease (PID). PID is a known cause of ectopic pregnancy and infertility. Ectopic pregnancy is an obstetric emergency and requires surgery to prevent serious complications for the mother, including a risk of death.

Some research published in 2011 suggests chlamydia also may contribute to miscarriage in the first trimester. Like all bacterial infections, chlamydia is treated with antibiotics. Condoms can protect you against chlamydia.


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). Gonorrhea 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.

Human Immunodeficiency Virus (HIV)

In the past, HIV infection was thought to dramatically increase the risk of miscarriage. Since the emergence of routine testing of pregnant women and more effective drug treatment, however, HIV-positive women are usually able to have a healthy, full-term baby.

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.

Herpes (HSV)

Herpes, another sexually transmitted infection, is a common viral infection that can cause painful sores on the genitals or mouth. A 2016 review study says the link between miscarriage and herpes infections is controversial. There does not appear to be an increased risk of pregnancy loss with HSV. There is a risk of the fetus contracting HSV during birth, however, so medication may be given in the weeks leading up to birth. If a woman has active herpes lesions at the time of labor, physicians recommend a c-section for delivery.


Syphilis is a sexually transmitted infection that can be easily treated with antibiotics. Because it is one of the most dangerous STIs to have during pregnancy, women are routinely screened for it during 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.

E. Coli

Although E. coli lives in everyone’s intestinal tracts, 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. There is a risk of miscarriage associated with certain E. coli infections. The best way to avoid E. coli is to follow proper food-handling techniques and to wash your hands frequently, especially before eating or touching your mouth.


Listeria is a bacteria found in certain kinds of foods. It is most commonly associated with unpasteurized cheeses, although it can 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. It is avoidable through proper food handling, good hand-washing, and avoiding foods known to carry higher risk of listeria infection while pregnant. Stay away from:

  • Hot dogs, lunch meats, cold cuts (when served chilled or at room temperature; heat to internal temperature of 74°C [165°F] or steaming hot)
  • Refrigerated pâté and meat spreads
  • Refrigerated smoked seafood
  • Raw (unpasteurized) milk
  • 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, skin should be washed thoroughly in running tap water, even if it will be peeled or cut)


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. Infection can be avoided through good food-handling techniques and thorough hand-washing.


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 toxoplasmosis). As a result, many obstetricians recommend that women avoid cleaning litter boxes during pregnancy. Toxoplasmosis also can be contracted by eating undercooked meat, but good food-handling techniques can all but eliminate the risk of contracting a food-borne illness.

Chickenpox (Varicella)

Although most adults are immune to chickenpox (through vaccination, or previously having the disease), a limited number of pregnant women can contract the virus. 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 mom contracts varicella within a few days of delivery. This can lead to neonatal varicella, which carries some risk of death for newborns, especially if they're premature.

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 covering your mouth and nose with your elbow when you sneeze.

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


Little information is available about the coronavirus, COVID-19, and its effect on pregnancy loss. However, pregnancy loss has been observed in related coronaviruses (such as SARS and MERS). In June 2020, the Centers for Disease Control and Prevention suggested that pregnant patients may be at increased risk for preterm birth and/or certain manifestations of severe illness if they contract COVID-19.

Reduce your risk of contracting COVID-19 by limiting interactions with others whenever possible, wearing a cloth face covering when you are in public, and washing your hands frequently. Talk with your healthcare provider about any concerns you have.


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, which has a risk of serious, lifetime complications such as microcephaly, developmental delays, or vision and hearing problems. There is also a risk of death for infants born infected with CMV.


There are many forms of hepatitis, but only one, Hepatitis E, is associated with a risk of death for both mother and baby. Hepatitis E is extremely rare in the United States. If a woman becomes infected with viral hepatitis for the first time while in her third trimester of pregnancy, she is at risk for preterm labor or delivery. Some forms of hepatitis can be passed on to a developing fetus and can cause long-term health complications.

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 a person has been bitten by a tick usually has a characteristic bulls-eye pattern around the bite which helps doctors identify potential Lyme disease. It has many long-term health effects if it is not diagnosed and treated early, but there is no conclusive evidence that pregnant women have an increased risk of pregnancy loss due to Lyme disease if they are being treated with antibiotics.


A common childhood illness, also known as fifth disease, parvovirus is not concerning for most adults. Pregnant women exposed to parvovirus usually have a mild course of the illness. Less than 5% of pregnant women 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 generally mild infection that people recover from with no long-term effects. It is covered by the MMR vaccine, and a mother’s immunity is usually tested at the first prenatal visit. If, however, a woman contracts rubella during pregnancy, there is a high risk of congenital birth defects, miscarriage, or stillbirth.

Zika Virus

Zika virus is an infection spread by mosquitoes that tends to show mild symptoms. However, it is known to cause microcephaly, a serious birth defect in which a baby's head is smaller than expected, which is why health officials recommend not traveling to areas where the virus is common during pregnancy (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 its true risk. 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.


Like Zika, 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 women are three times more likely to develop severe infections, and 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.

Dengue Fever

Though it's rare in the U.S., dengue fever is known to be the most common mosquito-borne infection worldwide. While researchers say its relationship to miscarriage is unknown, transmission to fetuses and pregnancy losses 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, and the infection usually clears within two to seven days.


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. Although it's a rare infection that can be treated with antibiotics, research has shown that it can pose a risk of miscarriage in pregnant women who become infected and do not treat it promptly.

A Word From Verywell

While you may not be at risk for certain conditions, it's important to be aware of infections that can potentially cause miscarriage or any other pregnancy complications, and to not skip or miss any prenatal appointments if possible. Talk to your doctor if you have any concerns or are experiencing any unusual symptoms.

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