Primary CMV infection during pregnancy
The rate of seroconversion of seronegative women during pregnancy has been stated to range between 1–7%, with 40–60% of women in the UK already likely to be seropositive.
Intrauterine infection occurs after primary maternal infection in all three trimesters with overall approximately 37% of neonates being born with congenital infection:
- the rate of fetal transmission appears to increase with advancing gestation (34.8% in 1st trimester, 42% in 2nd trimester and 58.6% in the 3rd trimester)
- approximately 10% of these neonates will have clinical manifestations of CMV
- culture-positive infants with no stigmata of the disease are still at risk of sequelae; 5–15% of CMV-infected infants will develop significant hearing loss by the time they are 2 years old.
It is not clear why primary infection does not cross the placenta in all women. There is some suggestion and evidence that mothers who are able to mount a strong immune response may be able to moderate the infection.
Primary infection during pregnancy may lead to early miscarriage; however, the magnitude of this problem is still unclear.
Neonates born with symptoms of intrauterine CMV infection may have some or all of the following problems:
- fetal growth restriction
- thrombocytopenic purpura
The outlook for such children is poor:
- the vast majority suffer severe mental impairment and/or hearing loss
- those born without symptoms at birth do not necessarily escape the damage of CMV
- approximately 15% of children develop symptoms later, with the brain and inner ear being major target organs.