Infections that are merely inconvenient in adults and older children can be devastating to the developing fetus or newborn. But with careful screening and the right knowledge, it’s often possible to prevent transmission to the infant. Last month, we looked at the screening and treatment of bacterial and parasitical infections. This month, we’ll consider viruses.

Hepatitis A, B and C virus (HAV, HBV and HCV)

A pregnant woman with HAV can only transmit the virus to the newborn by the usual fecal/oral routes, as vertical transmission has never been observed. Immunization and/or gammaglobulin treatment in pregnancy is safe and may confer some protection for the newborn.

Women who are acutely infected with HBV or those who are carriers can transmit the virus to the newborn at the time of delivery but not transplacentally. The vertical transmission risk depends on the stage of maternal infection. The majority of cases (95%) can be prevented by using HBV immunoglobulin (HBIG) and vaccine administered at birth to the neonate, followed by two additional doses at 1 and 6 months. The HBIG should be administered immediately after birth, and the first dose of the vaccine within 12 hours.

It seems that pregnancy has no effect on the progression of HCV. Newborns have an estimated 8% risk of being contaminated during pregnancy and delivery. The benefit of elective caesarean delivery in preventing perinatal HCV infection hasn’t been adequately studied. Treatments for HCV are contraindicated in pregnancy. Breastfeeding is considered safe, unless patients present cracked or bleeding nipples. Screening isn’t currently recommended for women without risk factors.

Human immunodeficiency virus (HIV)

Most cases of pediatric AIDS result from vertical transmission. AIDS continues to be a leading cause of death in children aged one to four years old. Earlier studies demonstrated the effectiveness of prenatal screening, and during the first prenatal visit all patients should be offered appropriate counselling and HIV antibody testing after informed consent. Antiretroviral therapy in HIV-infected pregnant women is critical to lower vertical transmission, but the risk is never zero, even when HIV RNA is below detectable levels.

Treatment relies on a combination of antiretroviral agents to obtain maximal suppression of viral replication. Vertical transmission can be reduced from 25% to less than 1% if viral load is effectively suppressed prior to delivery. It’s important to inform women about the potential side effects of the treatment, the importance of strict compliance and need for close monitoring. If HIV viral load is undetectable at the time of delivery, the choice between vaginal
or caesarean delivery will depend solely on obstetric conditions. If viral load is greater than 1,000 copies/ml a caesarean section is usually recommended to reduce the risk of vertical transmission. Breastfeeding is contraindicated as HIV can be transmitted through breast milk.

Varicella zoster virus (chickenpox)

Because varicella is common in childhood, the majority of women of childbearing age are already immune to the virus. Serologic proof isn’t required as a positive history provides reliable evidence of immunity. In case of doubt when contact occurs, pregnant women should be tested for varicella IgG. The diagnosis is usually made clinically. Vertical transmission takes place in 10-15% of primary maternal infections. Fetal
disease is usually transient and asymptomatic but 2-3% of children infected in the first half of pregnancy develop fetal varicella syndrome, with skin scarring in a dermatomal distribution, ipsilateral limb hypoplasia, visceral, neurologic and eye lesions. Susceptible pregnant women should be counselled about the risks of exposure to varicella during pregnancy. Preconception counselling should include determination of varicella immunity and vaccination, if necessary.

Parvovirus B19 infection

Parvovirus B19 causes erythema infectiosum or the fifth disease. Most adult B19 infections are either asymptomatic or minimally symptomatic. However, congenital B19 infection may lead to excess fetal loss, profound fetal hemolytic anemia, cardiac failure and hydrops if maternal infection occurs between 9-20 weeks. The two most frequent reasons for B19 testing (since routine antenatal screening isn’t indicated) are a history of recent maternal exposure or sonographic diagnosis of fetal hydrops. The diagnosis is clinical but may be confirmed by an elevated titer of IgM in serum or with PCR. If infection is confirmed during pregnancy, the fetus should be monitored for signs of hydrops by ultrasound examination.

Measles

Routine screening tests for measles immunity aren’t recommended but contracting the disease during pregnancy has a significant effect on the perinatal outcome, with consequences such as frequent abortions, premature labour, and increased risk of fetal or neonatal death. In the first 2 months of pregnancy, measles is associated within a 50% spontaneous abortion rate; infection in the third month results in a 20%
fetal loss rate. The overall perinatal mortality is about 10%. The infection in the newborn may be mild, severe or rapidly fatal. Clinical diagnosis is effective. Pregnant nonimmune women who are exposed to measles should be given the appropriate immunoglobulin. Measles vaccination is contraindicated during pregnancy but should be given to susceptible women at least 28 days before pregnancy or immediately after delivery.

Mumps

Because of the widespread use of the mumps vaccine (MMR) in pediatric immunization programs, mumps infection in pregnancy is very rare. During pregnancy, mumps increases the risk of spontaneous abortions and embryonic or fetal death. Perinatal infection consequent to vertical transmission is uncommon and not associated with higher risk of congenital anomalies.

Rubella

Rubella is a systemic disease generally preventable by vaccination. Age is the most important determinant of the severity of rubella. Postnatally acquired disease is usually innocuous, whereas fetal rubella can be devastating. If infection occurs in the first trimester of pregnancy, the risk of fetal infection and damage (including cardiac and CNS abnormalities with associated long-term disabilities) is high but it falls steeply becoming negligible after 16 weeks. The clinical diagnosis of rubella isn’t reliable; therefore serology (IgG and IgM titers) is the test of choice. If recent infection is suspected, prenatal diagnosis can be performed using amniocentesis to detect rubella RNA by reverse transcriptase-PCR and fetal blood sampling for IgM and RNA. Women who remain susceptible to rubella should receive MMR vaccine postpartum.

Cytomegalovirus (CMV)

CMV is the most common cause of congenital infection in developed countries, affecting about 1 in 150 neonates. Unlike most viral infections, CMV may be transmitted to the fetus during either a primary infection or reactivation. Most patients with congenital CMV infection are asymptomatic, but 1 in 750 live-born children affected will present CMV inclusion disease (usually following a CMV primary infection) characterized by jaundice, hepatosplenomegaly, thrombocytopenia, purpura, microcephaly, periventricular CNS calcification, mental retardation and motor disability. There is no vaccine or treatment that can be given during pregnancy. If primary maternal infection is suspected serological and liver function tests as well as a blood film will usually confirm the diagnosis. In case of likely recent CMV infection (especially in the first trimester) amniocentesis should be considered to determine whether the fetus is infected. Antenatal screening for CMV infection isn’t part of routine tests.

Herpes simplex virus (HSV)

Both herpes virus type 1 and type 2 can lead to congenital malformations including organomegaly, bleeding and CNS abnormalities if the fetus becomes infected. The risk of vertical transmission is greatest during primary maternal infection, and if acquired in the third trimester of pregnancy. Neonatal transmission during delivery is much more common than intrauterine infection, which is rare. There’s no evidence that routine serotesting in pregnancy can decrease the risk of neonatal herpes.

Recurrent genital infection during pregnancy poses low risk of transmission. It’s still unknown whether prophylaxis decreases the incidence of neonatal infection; but because it reduces viral shedding at time of delivery it also
reduces the need for surgical delivery. More research on the safety of prophylaxis to the unborn child is needed.

Diagnosis requires a careful assessment of clinical features, culture or PCR of genital sites and type-specific serology. Counselling on primary prevention, based on risk reduction behaviours, is important for all women who present for pregnancy care. Primary infection in pregnancy warrants treatment with acyclovir and cesarean section for delivery. Caesarean delivery substantially decreases the vertical transmission risk, but neonates can still be infected, even when the c-section is performed before rupture of membranes.

Human papillomavirus (HPV)

Pregnancy favours the growth of HPV genital warts on the vulva, perianal area, vaginal walls and the cervix. Infants and children when exposed during delivery to genital HPV types 6 and 11 can develop recurrent respiratory papillomatosis (RRP) characterized by respiratory tract lesions, especially of the vocal cord. RRP is rare due to low vertical transmission rates, even though maternal HPV prevalence is high. Caesarean section isn’t recommended to reduce vertical transmission. Women should be reassured that genital warts may proliferate, reappear and become friable in pregnancy.

Current thinking leans toward deferring treatment in the expectant mother due to poor response, and to adverse effect of drugs such as podophyllin, which is contra-indicated in pregnancy. If the patient insists on being treated, trichloroacetic acid, cryotherapy, CO2 laser and surgical excision are the available options. Prevention of HPV infection includes the same recommendations used for all sexually transmitted diseases, except that condom use doesn’t seem to help reduce transmission.

Conclusion

Although there’s been substantial progress in the prevention and control of infections in the general population, some still pose significant threats to pregnant women and their unborn children. Many STDs in particular remain significant public health concerns. Fortunately, vertically transmission can be reduced, if not prevented, when detected by routine antenatal screening.

More often than not, the management of infections in mothers-to-be will differ from that recommended for other groups. The physician must be familiar with the limitations and specific recommendations that apply in pregnancy, to attain the ultimate goal of improved outcomes for both mothers and their infants.