Risk Of Maternal Infection During Pregnancy

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Varicella can be an extremely serious disease in pregnant women. Fortunately, widespread use of vaccine is likely to decrease the overall incidence of varicella, including during pregnancy, because of individual and herd immunity. Eventually, it is hoped that widespread immunization of children will lead to only rare susceptibility during the childbearing years, as well as little circulation of the wild-type virus. This situation would be projected to make varicella in pregnancy extremely rare, as has occurred with rubella in pregnant women because of routine administration of rubella vaccine.

In the prevaccine era in the United States, it was estimated that there were 240-2400 annual cases of varicella in pregnant women (7). This is only an estimate because varicella is not a reportable disease nationally. The usual scenario is that if a pregnant woman contracts varicella, it is usually transmitted from her children, who were exposed to other children with chickenpox at school or day care. In the prevaccine era, the annual rate of varicella in children under the age of 10 years was 10% per year. Varicella is highly contagious, with an attack rate approaching 90% following a household exposure to the illness. Because varicella is so contagious in families, it makes the likelihood of contracting varicella for a susceptible woman with a young child attending school on the order of 5% during her pregnancy. The literature is replete with cases of severe varicella in pregnant women that proved fatal or near-fatal. Varicella is estimated to be 25 times more likely to be severe in adults than in children. There is thought to be an even greater risk associated with pregnancy, particularly during the third trimester. Presumably, this is caused by maternal immunosuppression, which is most intense during this period (7).

Most adults born in the continental United States are immune to varicella, even if they believe themselves to be susceptible. Individuals born in countries with tropical climates, however, are often susceptible to varicella, particularly if they moved into an area with a temperate climate as an adult (8). Therefore, it is likely that women who were born in the Caribbean, the Philippines, or Southeast Asia are likely to be varicella susceptible if they have no history of the illness. Ideally, such young women should have antibody testing before they become pregnant so that they can be immunized before pregnancy.

There is little information on the risk of developing zoster during pregnancy. A few studies have suggested that the incidence is about the same as that of varicella in pregnancy (7). The course of illness is not more severe in pregnant women, and as is discussed next, there is little if any risk to the fetus and newborn infant.

Fig. 1. Diagrammatic representation of transmission of varicella-zoster virus (VZV) and VZV antibody to the fetus in maternal varicella near term. (1) When the infant is born during the maternal incubation period, no varicella occurs unless the infant is exposed postnatally to the infection. (2) When the infant is born 0-4 days after onset of maternal varicella, disseminated varicella may develop because the infection will not be modified by maternal antibody. The onset of the varicella occurs between 5 and 10 days of age. (3) Infants born 5 days or more after maternal varicella receive maternal antibody, which leads to mild infection. This diagram is based on 50 newborn infants with varicella. (From ref. 15 with permission.)

Fig. 1. Diagrammatic representation of transmission of varicella-zoster virus (VZV) and VZV antibody to the fetus in maternal varicella near term. (1) When the infant is born during the maternal incubation period, no varicella occurs unless the infant is exposed postnatally to the infection. (2) When the infant is born 0-4 days after onset of maternal varicella, disseminated varicella may develop because the infection will not be modified by maternal antibody. The onset of the varicella occurs between 5 and 10 days of age. (3) Infants born 5 days or more after maternal varicella receive maternal antibody, which leads to mild infection. This diagram is based on 50 newborn infants with varicella. (From ref. 15 with permission.)

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Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

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