1. Are pregnant women immunocompromised?

Pregnancy presents a unique immunologic situation in which two individuals with different genetic makeups coexist with no deleterious immune response. However, this is not accomplished through immunosuppression of the mother. All objective measures of maternal immunocompetence show little or no change with pregnancy. Infections (e.g., pneumonia, pyelonephritis) may be more severe in pregnancy, but this is due to anatomic and physiologic changes associated with pregnancy, not a poorly functioning immune system.

2. Why are infections in pregnancy important?

Infections during pregnancy are important for two reasons. Some infections can cause significant maternal morbidity or even mortality (e.g., pneumococcal pneumonia). This is obviously deleterious to the mother and can indirectly harm the fetus. Other infections may be of little or no clinical significance to the mother but can harm the fetus through fetal or placental infection (e.g., toxoplasmosis).

3. What neonatal conditions are caused by group B streptococcus? How can they be prevented?

Group B strep can lead to two different clinical entities in the neonate: early-onset infection (characterized by septicemia) and late-onset disease (usually meningitis). Both of these infections occur more commonly in preterm infants, but they can affect term newborns.

A variety of prevention strategies featuring screening cultures and antibiotic regimens have been advocated. Currently there are two strategies that have the support of the American College of Obstetricians and Gynecologists, the American Academy of Pediatrics, and the Centers for Disease Control and Prevention:

(1) Screen all pregnant women between 35 and 37 weeks’ gestation and treat those women with positive cultures with ampicillin or penicillin in labor.

(2) The second strategy omits screening cultures and relies instead on identifying women with risk factors for neonatal infection. These risk factors are: preterm (< 37 weeks) delivery, rupture of membranes for more than 18 hours, interpartum fever (≥ 38°C), or a prior child affected with group B strep. In addition, both strategies treat all women with a history of group B strep bacteriuria as these women tend to have persistent high colony counts. Both strategies effectively reduce-but do not eliminate-the risk of neonatal disease.

4. Which common genital infections are implicated in preterm birth?

Bacterial vaginosis has been associated with preterm birth, and treatment of bacterial vaginosis in high-risk women has been shown in some studies to reduce the incidence of preterm birth. Other genital infections, such as Trichomonas, gonorrhea, and Chlamydia, have been inconsistently associated with preterm premature rupture of membranes and/or preterm delivery.

5. What are examples of infections with minimal maternal effects but the potential for significant fetal compromise?

Parvovirus infection, cytomegalovirus (CMV) infection, and toxoplasmosis.

6. What maternal and fetal effects are caused by parvovirus?

Parvovirus infection, also known as fifth disease, is a relatively common infection that is usually asymptomatic or mildly symptomatic in adults. Most infections of pregnant women occur following exposure to infected children. Although the effect on the mother is insignificant, parvovirus can infect the fetus and lead to anemia with subsequent fetal hydrops and even death. The diagnosis is made by serial maternal serologies. If fetal infection is likely and ultrasound shows fetal hydrops, in utero transfusion may be necessary.

7. How does CMV affect the fetus?

CMV is a common pathogen. The majority of adults have detectable antibodies demonstrating prior exposure. Unfortunately, prior infection and the development of antibodies doesn’t provide protection from subsequent infections. Given this lack of protection and the ubiquitous nature of the organism, infections during pregnancy are not uncommon. The mother is asymptomatic or mildly symptomatic. The fetus, however, can suffer severe effects involving the nervous system. Fetal growth restriction can also occur as a result of in utero cytomegalovirus infection.

8. Should pregnant women be screened for antibodies to cytomegalovirus?

No. Most women have antibodies, and antibodies detected during screening almost always represent prior disease, which poses no risk to the mother or fetus. Moreover, the presence of antibodies does not provide immunity against future infection. Even in cases of suspected acute maternal infection, antibody titers are of limited value.

9. What is the significance of toxoplasmosis in pregnancy?

Toxoplasma gondii is a parasite that is transmitted by ingestion of infected meat or exposure to infected cat feces. In immunocompetent adults, the infection is inconsequential. If maternal infection occurs during pregnancy, however, fetal infection can occur. The later in pregnancy the maternal infection occurs, the more likely the infection will pass to the fetus. Conversely, it is fetal infections that occur early in gestation that are most likely to cause fetal sequelae. There is a wide range of fetal effects from toxoplasmosis, including subclinical disease, growth retardation, and severe effects on multiple systems including the central nervous system (CNS). If the diagnosis is made antenatally, antiparasitic therapy can be initiated to prevent sequelae.

Prior maternal exposure to T. gondii provides protection against fetal infection. Simple preventative steps should be emphasized to all pregnant women. These include avoiding cat litter, proper handwashing before handling food, and avoiding poorly prepared meat.

10. Does maternal varicella infection pose risks during pregnancy? What about herpes zoster?

Acute varicella infection (or chickenpox) and herpes zoster (or shingles) are both caused by the varicella-zoster virus. The initial infection with the virus causes varicella usually involving the skin alone. Subsequent reactivation of the dormant virus can lead to zoster usually affecting a single, unilateral dermatome.

Acute maternal varicella infection can be a severe illness for both the mother and the fetus. Adults generally suffer greater morbidity from varicella infection than do children or adolescents. Pneumonia in particular poses a risk to maternal health. Fetal effects can include skeletal deformities, as well as effects on the eyes, CNS, and kidneys. There is risk to the fetus only if maternal infection occurs during one of two time periods: between 13 and 20 weeks, or at the time of delivery. Infection in the second trimester can cause congenital disease; peripartum exposure can lead to neonatal varicella infection.

Zoster outbreaks during pregnancy cause maternal discomfort, but do not pose a risk to the fetus. However, a susceptible woman can develop a varicella outbreak if she is exposed to an individual with active zoster.

Key points: infections during pregnancy

  • Maternal parvovirus infection can lead to fetal anemia, hydrops, and even IUFD.
  • Prenatal testing for CMV antibodies is of little value because it is not reliable in diagnosing acute infection and they do not confer immunity.
  • The main risk to the fetus of a woman with HIV is neonatal infection; risk is decreased to <5% with medical treatment during pregnancy, intrapartum, and for the neonate, and with a cesarean section if detectable viral load.
  • Women with active HSV at the time of delivery should undergo a cesarean section to prevent neonatal transmission.
  • Rubella and varicella vaccines cannot be given during pregnancy but should be given to non-immune women before or between pregnancies to prevent fetal/neonatal infections.

11. Can varicella-zoster infection be prevented?

Varicella infection can be prevented through immunization of infected individuals or by the administration of varicella-zoster immunoglobulin (VZIG) to susceptible individuals who are exposed to the virus. The vaccine should not be administered during pregnancy. VZIG can and should be administered in appropriate situations to susceptible pregnant women. Not only will the mother be protected from the effects of the disease, but her fetus will also benefit by avoiding the potential for in utero or neonatal disease.

12. How does infection with the human immunodeficiency virus (HIV) impact pregnancy?

As with all maternal infections during pregnancy, there are maternal and fetal concerns. For the mother, the major health concern is control of the disease. For the fetus, the main concern is the prevention of vertical transmission. Pregnancy does not appear to worsen the disease in the mother, nor does the presence of maternal infection appear to carry risk to the fetus outside of the risk of neonatal infection.

13. Can antiretroviral therapy be safely used in pregnancy?

There are obvious concerns about the use of antiviral agents to treat HIV infection in pregnant mothers. The agents used can be toxic, and there is limited human data regarding their safety in pregnancy. However, the safety concerns need to be balanced against the potential benefit to mother and baby. Depending on the severity of maternal disease, medical therapy may provide significant maternal benefit. For the baby, the benefit is more straightforward. The likelihood of vertical transmission is directly related to maternal viral load, and antiviral therapy reduces viral load. Pregnant women should be offered medical therapy even if they have a relatively low disease burden (as evidenced by CD4 counts and viral counts). Current management of HIV infection usually includes multi-drug therapy.

14. What steps can be taken to reduce the risk of vertical transmission?

Prevention of vertical transmission is accomplished through a multi-stage strategy. First, women with significant viral load should receive medical therapy during the antepartum period. Second, if the maternal viral load is greater than 1000 copies per mL, cesarean section should be offered. Third, women with HIV should not breastfeed.

Cesarean section only appears to reduce the rate of transmission in women with higher viral loads. The benefit of cesarean section applies even if the membranes are ruptured.

Together, these approaches should reduce the risk of vertical transmission to < 5%. This compares with a transmission rate of 15-25% in women who receive no treatment and who undergo vaginal delivery.

15. Should pregnant women be routinely screened for HIV infection?

Yes. There is a consensus that all pregnant women should be offered screening for HIV. Targeted testing only of women with risk factors misses too many cases. This testing should be voluntary and accompanied by appropriate counseling.

16. What is the significance of rubella in pregnancy?

Rubella causes German measles, which is a minor maternal illness, but which can cause significant fetal illness leading to severe effects on multiple systems, including the heart and nervous system. Rubella can also lead to growth restriction. Fetal infection is more likely if maternal illness occurs early in pregnancy. Fetal infection in the first trimester is also more likely to lead to serious sequelae.

Fortunately, maternal infection and its sequelae can be largely prevented through immunization of women of child-bearing age. Women should be assessed for immunity, and vaccination should be recommended to susceptible individuals. This should be a part of preconception counseling and is required by many states prior to issuing a marriage license.

17. What are the fetal effects of congenital syphilis?

Fetal infection with Treponema pallidum can cause significant sequelae, including hydrops and hepatosplenomegaly. It can also lead to stillbirth. Fetal effects can be prevented by screening pregnant women for syphilis and treating appropriately based on the stage of the illness. Treatment during pregnancy is always with penicillin. Women who are believed to be allergic should be tested and desensitized if necessary.

The prevalence of syphilis in the general population has declined in the last decade. This development, combined with effective screening, should make congenital syphilis very rare.

18. How does herpes simplex virus (HSV) affect pregnancy?

HSV is a relatively common genital infection. This virus causes an initial infection and is then latent. Some infected women only suffer the initial, or primary, outbreak, but many women experience secondary outbreaks as frequently as several times each year. The main concern with maternal HSV infection is transmission to the newborn. Transmission only occurs if the mother is experiencing an outbreak around the time of delivery. Neonatal disease ranges from asymptomatic infection to disseminated disease and death.

19. How is transmission of HSV to the fetus/newborn prevented?

If at the time of labor she is symptomatic (with a viral prodrome) or has a visible genital herpes lesion, then cesarean section is recommended. The risk to the newborn is much more significant if the mother is experiencing an initial outbreak as opposed to a recurrence. In recurrent or secondary outbreaks, maternal antibodies likely provide some passive immunity to the newborn. Although the risk is much lower with secondary outbreaks, cesarean section is still routinely recommended.

The frequency of secondary herpes outbreaks can be reduced with daily medication with antivirals (acyclovir and others). If a woman has frequent outbreaks before or during pregnancy, many providers use daily prophylaxis beginning at 36 weeks to reduce the likelihood of a peripartum outbreak and to avoid the need for a cesarean section.

20. For which infections should pregnant women be screened?

Currently, universal screening is only conducted for a limited number of diseases: HIV, syphilis, and group B streptococcus. Pregnant women are also screened for immunity to rubella, but this screening is done to identify susceptible individuals for postpartum immunization, not for disease identification.

There are advocates for screening for several other diseases (e.g., toxoplasmosis, bacterial vaginosis). When considering use of a screening test, make your decison based on its accuracy (as defined by sensitivity and specificity), the prevalence of the disease, the severity of the disease, the ability to improve outcome through early identification, and the costs (of screening, confirmation, and treatment). The availability of a screening test doesn’t necessarily warrant its universal application.

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