Infections in Pregnancy

Written by the Healthline Editorial Team | Published on March 15, 2012
Medically Reviewed by Dominic Adam Marchiano, MD

Understanding Infections

For most women, pregnancy is a normal and healthy state. But, pregnancy can also make women more prone to certain infections. Further, pregnancy may make these infections more severe than they would otherwise be-even mild infections can lead to serious illness.

Some infections that occur during pregnancy pose a risk primarily to the mother. Others, which can be transmitted to the fetus, present serious risks for the baby as well. Some infections during pregnancy can even lead to miscarriage, preterm labor, birth defects, or maternal death. To complicate matters, the drugs used to treat infections can cause serious side effects, especially for the unborn child.

Why Are Pregnant Women More Susceptible to Infection?

Pregnancy affects every physiological system in your body. Changes in immune function and hormonal balance can make you more vulnerable to infections and serious complications. Labor and delivery are especially susceptible times for both you and your baby.

Effects of Pregnancy on Immunity

The immune system defends the body against invaders, ranging from bacteria, viruses, and other potential causes of infection to cancer cells or transplanted organs. A complex collection of players works together to identify and eliminate intruders.

In fighting infection, the body relies on several layers of defense. These include general barriers, such as the skin and mucous membranes (which line body cavities that open to the exterior, namely the mouth, nose, and reproductive organs) as well as cells whose job it is to swallow and destroy bacteria or to kill infected cells. The immune system includes cells that recognize specific antigens (substances that invoke an immune response) and cells that produce antibodies to attack antigens.

During pregnancy, your immune system changes so that it can protect both you and your baby from disease. Different parts of your immune system are enhanced while others are suppressed. This creates a balance that can prevent infection in the fetus without compromising the defenses that keep you healthy as well.

Changes in a woman's immune system during pregnancy include:

  • increased production of macrophages (cells that destroy bacteria). this improves antibody response and helps to protect you against bacteria-though they do not guarantee protection against bacterial infections;
  • decreased activity of NK cells ("natural killer" white blood cells, which kill cells that have been infected with a virus or that are part of a tumor);
  • decreased activity of T cells, which help to control infections caused by viruses; and
  • decreased production of cytokines (which are released from immune cells to recruit other cells to help fight infection).

These alterations protect your baby from your body's defenses because, in theory, your baby is like an organ transplant that your body sees as part "self" and part "foreign." However, due to depressed T cell function, you are more prone to opportunistic infections (those that do not cause disease when the immune system is normal) and viral infections. In fact, the incidence of viral illness, the intensity of viral attack, the severity of illness, and the rate of death are all higher in pregnant women than in non-pregnant women.

Infections Related to Body Changes

In addition to the immunologic changes that occur during pregnancy, hormonal changes can predispose you to infection. These effects are most pronounced in the urinary tract, which is made up of the kidneys (organs that produce urine), ureters (tubes that carry urine from the kidneys to the bladder), bladder (where urine is stored), and urethra (tube that transports urine out of the body). As the uterus enlarges during pregnancy, it compresses the ureters. Meanwhile, increased secretion of the hormone progesterone relaxes the ureter and bladder muscles. As a result, urine may stay in the bladder too long, which increases your susceptibility to urinary tract infections (UTIs).

Candidiasis (yeast infection) is another example; the effect of increased estrogen in the reproductive tract predisposes you to frequent yeast infections. And, because your lungs contain more fluid during pregnancy and pressure on the lungs from the abdomen makes it harder to clear this fluid, you are also more likely to develop pneumonia. This is true because the extra fluid stimulates bacterial growth and hinders your body's ability to resist infection.

Risks for Mother and Baby

Some infections that occur during pregnancy, such as urinary tract infections, vaginitis, and postpartum infection, pose problems primarily for the mother. Other infections are particularly troublesome for the baby. Cytomegalovirus infection, toxoplasmosis, and parvovirus, for example, can all be transmitted from mother to baby and lead to serious injury. Unfortunately, no effective treatment yet exists for congenital (existing at birth) cytomegalovirus infection. Antibiotics are available that have moderate activity against toxoplasmosis. Although no antibiotic therapy is active against parvovirus, there is an effective intervention (intrauterine blood transfusion) for a baby who has developed this infection.

Other infections- syphilis, listeriosis, hepatitis, and HIV infection-present grave risks for both mother and baby. Antibiotics are effective against maternal and fetal syphilis, if the infection is diagnosed in a timely manner. Though there are no antibiotics with specific activity against viral hepatitis, vaccines are now available to help prevent hepatitis A and B infections.

HIV infection in pregnant women is a problem of epidemic proportions. However, new multi-drug combinations now significantly prolong the life span and improve the quality of life of infected patients. Along with cesarean delivery before the onset of labor, these drug therapies have been remarkably effective in reducing the rate of transmission of HIV infection from pregnant women to their babies.

The Importance of Knowledge and Ongoing Care

Clearly, the relationship between you and your doctor is vital during your pregnancy. Knowing about the added risk of infection during pregnancy and the potential harm to you and your baby will help you prevent transmission and receive effective treatment should an infection arise. Most importantly, you should have ongoing care throughout your pregnancy from a well-informed, skilled physician whom you trust. If you have any questions during your pregnancy, do not hesitate to ask your doctor.

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