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Discuss the monitoring of virus infections in pregnancy

 

Several viruses from different virus families can cross the placenta to cause congenital infection in the fetus, or infect the baby perinatally as it passes through the birth canal of the mother. Occasionally, this may result in severe consequences for the baby. Therefore, it is essential to investigate any febrile diseases or those with a rash during pregnancy, so that appropriate steps may be taken. The following virus infections may be transmitted vertically from the mother to child.

  1. Rubella

  2. Cytomegalovirus

  3. Herpes Simplex

  4. Varicella Zoster

  5. Enteroviruses

  6. Parvovirus

  7. HIV

  8. HBV

  9. Others eg. HCV, LCM

Rubella

Primary maternal rubella infection in the first trimester of pregnancy carries devastating consequences for the fetus. There is almost a 100% chance of developing severe congenital malformations if the infection occurred within the first eight weeks of pregnancy. Fortunately, primary rubella infection in the mother is usually symptomatic, presenting with a maculopapular rash, fever, and possibly arthralgia. Therefore, medical opinion is usually sought and the illness investigated by the laboratory. Termination of pregnancy is the usual recommendation for any laboratory confirmed cases of primary maternal rubella occurring in the first trimester of pregnancy.

Since primary rubella infection is usually symptomatic, there is little justification in the routine screening of the mother's blood for the presence of acute rubella infection in the first trimester of pregnancy. All suspected contacts with rubella in early pregnancy should be investigated. In many countries including the UK, the mother's blood which is taken at the antenatal booking clinic is screened for the presence of rubella antibodies and hence past immunity, and so that non-immune women may be offered rubella vaccination after birth.

CMV

In countries with a successful immunization policy against rubella, CMV has replaced rubella as the leading viral cause of mental handicap. Congenital infection may follow primary or recurrent CMV infection during any stage of pregnancy. Most congenital infections are asymptomatic. A minority (5-10%) of congenitally infected infants present with symptoms of cytomegalic inclusion disease. A further 5-10% of asymptomatic infants will develop late sequelae such as hearing defects later on. There is a 1 in 25 chance of an infant born with cytomegalic inclusion disease if the mother contracts a primary CMV infection during pregnancy. The actual figure for recurrent infection is unknown but the incidence of cytomegalic inclusion disease is much higher in infants congenitally infected following primary CMV infection than recurrent CMV infection.

Unlike rubella, most CMV infections, whether primary or recurrent, are asymptomatic. Occasionally, primary CMV infection may result in an infectious mononucleosis like syndrome. Therefore, in order to monitor for active CMV infection, one would have to take repeated urine specimens throughout pregnancy for CMV culture. Alternatively, one may screen for primary maternal infection only. A primary infection may be diagnosed in hitherto known seronegative women by carrying out repeated IgM tests throughout pregnancy. Both screening policies would involve a lot of manpower and resources and are not justifiable, unless one is prepared to recommend termination of pregnancy to all diagnosed cases of CMV infection during pregnancy.

HSV

Neonatal HSV infections occurs at an incidence of between 1 in 2500 to 1 in 10000 live births. Most infections are acquired by the infant as it passes through the birth canal of the mother. Genital herpes in the mother is an obvious predisposing factor, although the majority of infected infants are born to mothers who have no signs or symptoms of active infection at the time of delivery but in whom asymptomatic shredding of HSV occurs. Premature rupture of the membranes is also a risk factor. The indications for an elective caesarean section are controversial but the majority of obstetricians would recommend it in the presence of a florid primary maternal infection at the time of labour. Recurrence of genital herpes is not an indication for caesarean section. Since shredding of HSV from the genital tract is common and neonatal HSV is rare, there is no justification for the routine screening for HSV shredding in pregnant women. Florid primary genital herpes infection can be diagnosed by clinical recognition with or without laboratory confirmation.

Varicella-Zoster

Very rarely, varicella infection in early pregnancy may result in the virus crossing the placenta to cause a severe characteristic congenital varicella syndrome in the fetus. VZV may also cross the placenta in the end-stage of pregnancy to cause neonatal varicella, which may range from mild to severe. Varicella in the mother usually presents with a characteristic rash which could be confirmed by laboratory investigations. Contacts with known cases of varicella during pregnancy should be investigated by screening the mother for immunity against VZV. Non-immune mothers should be offered varicella-zoster immunoglobulin as a prophylaxis against infection.

Enteroviruses

Like VZV, enteroviruses can cross the placenta in the end-stage of pregnancy to cause a potentially severe disease in the neonate. Typically, the mother presents with a fever a few days before delivery. In this cause, faecal and other specimens from the mother should be cultured for enteroviruses. If enterovirus infection is confirmed, it may be opportune to give human normal immunoglobulin to the baby to reduce the severity of the infection.

Parvovirus

Parvovirus infection during pregnancy, especially the second trimester of pregnancy may lead to fetal distress and natural abortion by causing hydrops fetalis in the fetus. Parvovirus is not associated with any congenital defects and therefore there are no indications for the routine screening of parvovirus infection in pregnancy. Since parvovirus cause a similar clinical picture to rubella, it is important to exclude rubella infection.

HIV

The rate of vertical transmission of HIV varies from around 15% in Europe to up to 50% in some countries in Africa. The question of whether to or not to screen for HIV antibodies in women attending antenatal clinics is a very difficult one as it involves ethical and legal considerations. Such a policy would probably not be justified in low prevalence areas such as the U.K., where anonymous studies carried out on pregnant women showed a low prevalence. Antenatal screening may be justified in high prevalence areas such as Central Africa. Another argument in favour of screening is that anti-HIV agents given to the mother has now been shown to be effective in preventing the transmission of HIV to the infant.

HBV

There is a 80% chance of transmission of hepatitis B virus vertically from mother to child if the mother is an e antigen positive carrier. Most infected infants will become carriers and thus liable to develop cirrhosis and hepatocellular carcinoma later on in life. Most vertical infections occur perinatally and postexposure prophylaxis is possible with hepatitis B vaccine and immunoglobulin. Vertical transmission is the main mechanism for the maintenance of the high prevalence of hepatitis B in areas of high endemicity. Therefore, antenatal screening for hepatitis B surface antigen in pregnant women would be justified in areas of high prevalence. However, even in areas of low prevalence such as the U.K., there is movement towards the implementation of antenatal screening, so that infants of mothers who are hepatitis B positive may be protected by prophylaxis.

Others

Other viruses such as hepatitis C, Japanese B encephalitis, LCM virus and lassa fever have rarely been reported to cause congenital infections. Since such occurrences are rare, there are no indications for antenatal screening. One should however be aware of the possible effects on the fetus if such infections were diagnosed during pregnancy. HTLV-I may be transmitted vertically from the mother to child, usually via breast milk. In countries where HTLV-I infection is prevalent such as Japan, it may be beneficial to screen all pregnant women so that seropositive women can be advised against breast feeding once the child is born.

To conclude, the detection and monitoring of some virus infections in pregnancy such as HBV and HIV may lead to reduced chances of transmission of the virus to the fetus. However, in other cases such as CMV, the need for monitoring is less clear-cut as nothing could be done to stop transmission except by the termination of pregnancy.