Infection and Pregnancy Loss

Viral and Bacterial Infections and Their Role in Pregnancy Loss

There are many types of infections that can cause an increased risk of miscarriage, stillbirth, or neonatal death. Not every woman who gets ones of these infections will have a pregnancy loss. It is also worth noting that these infections are not the most common cause of pregnancy loss — chromosomal abnormalities are the number one cause. This 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.

Bacterial Vaginosis

Pregnant woman looking out a window
  emituu/iStock/Getty Images

Bacterial vaginosis (BV) is an excess growth of normal vaginal bacteria. BV is not a sexually transmitted disease, but as a vaginal infection, many women notice the characteristic “fishy” odor of BV after intercourse. However, sometimes there is no noticeable odor and often does not require treatment in non-pregnant women. In pregnancy, however, 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 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 contracting 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 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 routine testing of pregnant women and more effective drug treatment, however, HIV+ women are usually capable of having a healthy, full-term baby. There is no cure for HIV, but 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 any 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 STDs to have during pregnancy, women are routinely screened for it during prenatal care. Untreated, syphilis can lead to stillbirth of 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. 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 infection. 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 (recently, an outbreak of listeriosis was traced back to cantaloupe). Listeriosis (infection due to listeria exposure) has a known risk of miscarriage. It is avoidable through proper food handling and good hand-washing.


Salmonella is a bacteria which 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 lizard. 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 one of the infections with a known risk of miscarriage. It is commonly associated with being exposed to cat feces, which is why pregnant women used to be advised to avoid cats. Many obstetricians still 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.

Chicken Pox

Although most adults are immune to chicken pox (through vaccination, or previously having the disease), a limited number of pregnant women can contract the virus. The risk in pregnancy varies by how far along you are when you are exposed to chicken pox. There is little risk in the first trimester. Up to 36 weeks gestation, the risk to the fetus is small when the mother has chicken pox. However, 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 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 practice, like hand-washing and covering your mouth and nose with your elbow when you sneeze. Flu vaccine is also recommended for pregnant women to reduce the risk of potential complications from flu infection.


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, 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 an 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 bull’s-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. There is no conclusive evidence that pregnant women have an increased risk of pregnancy loss due to Lyme disease, especially 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 a 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.

Was this page helpful?

Article Sources

  1. McClure EM, Dudley DJ, Reddy UM, Goldenberg RL. Infectious causes of stillbirth: a clinical perspectiveClin Obstet Gynecol. 2010;53(3):635–645. doi:10.1097/GRF.0b013e3181eb6620

  2. American College of Obstetricians and Gynecologists. Repeated Miscarriages. Published May 2016.

  3. Işik G, Demirezen Ş, Dönmez HG, Beksaç MS. Bacterial vaginosis in association with spontaneous abortion and recurrent pregnancy lossesJ Cytol. 2016;33(3):135–140. doi:10.4103/0970-9371.188050

  4. Merck Manual Professional Version. Bacterial Vaginosis (BV). Updated September 2019.

  5. Centers for Disease Control and Prevention. Pelvic Inflammatory Disease (PID) - CDC Fact Sheet. Updated December 11, 2015.

  6. Baud D, Goy G, Jaton K, et al. Role of Chlamydia trachomatis in miscarriageEmerg Infect Dis. 2011;17(9):1630–1635. doi:10.3201/eid1709.100865

  7. Centers for Disease Control and Prevention. STDs during Pregnancy - CDC Fact Sheet (Detailed). Updated February 11, 2016.

  8. Wall KM, Haddad LB, Mehta CC, et al. Miscarriage among women in the United States Women's Interagency HIV Study, 1994-2017. Am J Obstet Gynecol. 2019;221(4):347.e1-347.e13. doi:10.1016/j.ajog.2019.05.034

  9. Giakoumelou S, Wheelhouse N, Cuschieri K, Entrican G, Howie SE, Horne AW. The role of infection in miscarriageHum Reprod Update. 2016;22(1):116–133. doi:10.1093/humupd/dmv041

  10. Straface G, Selmin A, Zanardo V, De Santis M, Ercoli A, Scambia G. Herpes simplex virus infection in pregnancyInfect Dis Obstet Gynecol. 2012;2012:385697. doi:10.1155/2012/385697

  11. Centers for Disease Control and Prevention. Syphilis. Updated May 22, 2019.

  12. Sacerdoti F, Scalise ML, Burdet J, Amaral MM, Franchi AM, Ibarra C. Shiga Toxin-Producing Escherichia coli Infections during PregnancyMicroorganisms. 2018;6(4):111. doi:10.3390/microorganisms6040111

  13. American College of Obstetricians and Gynecologists. Listeria and Pregnancy. Published June 2018.

  14. Tam C, Erebara A, Einarson A. Food-borne illnesses during pregnancy: prevention and treatmentCan Fam Physician. 2010;56(4):341–343.

  15. Centers for Disease Control and Prevention. Parasites - Toxoplasmosis (Toxoplasma infection). June 26, 2019.

  16. Blumental S, Lepage P. Management of varicella in neonates and infantsBMJ Paediatr Open. 2019;3(1):e000433. doi:10.1136/bmjpo-2019-000433

  17. Kerr SM, Parker SE, Mitchell AA, Tinker SC, Werler MM. Periconceptional maternal fever, folic acid intake, and the risk for neural tube defectsAnn Epidemiol. 2017;27(12):777–782.e1. doi:10.1016/j.annepidem.2017.10.010

  18. Centers for Disease Control and Prevention. Babies Born with Congenital Cytomegalovirus (CMV). Updated May 31, 2019.

  19. Chaudhry SA, Verma N, Koren G. Hepatitis E infection during pregnancyCan Fam Physician. 2015;61(7):607–608.

  20. Waddell LA, Greig J, Lindsay LR, Hinckley AF, Ogden NH. A systematic review on the impact of gestational Lyme disease in humans on the fetus and newbornPLoS One. 2018;13(11):e0207067. doi:10.1371/journal.pone.0207067

  21. Centers for Disease Control and Prevention. Pregnancy and Fifth Disease. Updated November 17, 2017.

  22. Centers for Disease Control and Prevention. Pregnancy and Rubella. Updated September 15, 2017.