Transplacental infection

Rubella

If a pregnant woman is exposed to primary rubella infection, especially in the first trimester, the baby may be born with one or a number of serious clinical features, including deafness, retinopathy, encephalopathy, deafness or a heart defect. The risk of congenital abnormality is greatest if the fetus is exposed to infection during the first 8 weeks of pregnancy, and this is evident in 85% of such babies (Hull and Johnston 1993). The risk gradually reduces with increasing gestation and is negligible after 22 weeks of pregnancy.

Toxoplasmosis

Toxoplasmosis is a parasitic infection caught from cat faeces and contaminated soil, raw or inadequately cooked meet and unpasteurised goats' milk products. It is thought that about half of the population will have been infected without realising it. If toxoplasmosis is contracted during pregnancy the risk of transplacental transmission is about four out of ten. Infection is most significant in early pregnancy but may affect the fetus at any stage. If maternal infection is confirmed during pregnancy, antibiotic therapy can reduce the risk of the fetus becoming infected. Infection could result in blindness or encephalopathy at birth, or the development of chorioretinitis in later life.

The practitioner examining the baby exposed to toxoplasmosis in utero, must refer it to a paediatrician for follow-up care.

Chicken pox

Chicken pox is caused by the herpes varicella zoster virus (HZV). Maternal primary infection in early pregnancy may lead to serious fetal anomalies (congenital varicella syndrome), including central nervous system damage and eye deformities, although these are rare. Neonatal morbidity is highest when the mother develops the rash in the week surrounding the birth, and it is associated with a mortality rate of approximately 30% (ACOG 1993). Babies born to infectious mothers should be referred to a paediatrician for possible treatment with acyclovir and/or vaccination.

HIV infection

There is no way of testing whether babies of HIV-infected mothers will ultimately develop the virus, for all such babies will have acquired antibodies via the placenta. It is only through long-term follow-up that HIV infection can be ruled out, and it is therefore important that such babies receive paediatric follow-up. Approximately one-third of babies will become infected, although infection cannot be diagnosed until the infant is 18 months old as maternal antibodies may persist until then. Breast feeding is contraindicated in the developed world, where the risk of transmission outweighs the benefits.

Cytomegalovirus (CMV)

CMV is the most common intrauterine infection, occurring in 0.42.4% of all live births (Seidel et al. 1997). The virus persists after primary infection and can be reactivated. It is estimated that between 1 % and 5% of pregnant women become infected, with approximately 50% of those pregnancies being affected by the virus. A wide range of malformations may be caused, including microcephaly, growth retardation and nerve deafness, but only 5% will have clinical signs at birth. If infection is confirmed during pregnancy, audiology follow-up may be indicated.

Listeria

The source of the bacteria responsible for this bacterial infection is soft cheeses, unpasteurised milk products and meat products requiring reheating. It may be acquired by the fetus via the placenta or during delivery. Those infants infected before birth usually present with symptoms of septicaemia soon after delivery, and the associated mortality rate is approximately 30%. However, where maternal infection is confirmed, antibiotic therapy may improve the outlook for the fetus. Offensive liquor and placental abscesses may have been noted at the delivery. Infants becoming infected after delivery often present with meningitis (Seidel et al. 1997) and have a better prognosis.

Congenital parvovirus B19

This virus when contracted by the mother may lead to spontaneous abortion or hydrops fetalis in about 1 % of those pregnancies that progress. Most maternal infections with this virus do not affect the developing fetus.

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