Cytomegalovirus in Pregnancy
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Direct answer
Cytomegalovirus is the commonest congenital infection, and the risk of fetal harm depends mainly on whether the mother has a primary or a non-primary infection, with primary infection transmitting far more often. Diagnosis combines maternal IgG avidity testing with fetal ultrasound and amniotic fluid PCR after about 21 weeks. Most congenitally infected newborns are asymptomatic, but sensorineural hearing loss can appear later, so every infected infant needs hearing follow-up.
What you must remember
- Primary infection: Seroconversion during pregnancy; transmission to the fetus is roughly one in three, and severe disease is more likely when infection is early.
- Non-primary infection: Reactivation or reinfection in a seropositive woman; transmission is much lower, at about 1 percent in widely cited series.
- Sonographic markers: Intrauterine growth restriction, ventriculomegaly, periventricular echogenicity, echogenic bowel, ascites, hepatosplenomegaly and placental thickening.
- Serology: Low IgG avidity suggests recent primary infection; an IgM result alone is not diagnostic.
- Confirmation: Amniotic fluid PCR for CMV DNA after about 21 weeks and at least six weeks after maternal infection.
- Congenital outcome: Most infected newborns are asymptomatic; a minority have hepatosplenomegaly, petechiae and thrombocytopenia at birth, and hearing loss can develop later.
- Treatment: Ganciclovir and valganciclovir are avoided in pregnancy; symptomatic newborns are treated with valganciclovir, usually for six months.
A stepwise pathway for suspected maternal infection
A pregnant woman with suspected new CMV infection is assessed in a fixed sequence, because a single test result rarely settles the question.
- Establish the serology: Send CMV IgG and IgM; a single IgM can persist for months, so its timing is unclear without a second sample.
- Test avidity: A low IgG avidity index suggests infection within the previous few months, while high avidity makes recent primary infection unlikely.
- Image the fetus: Serial growth scans and a detailed anomaly scan look for ventriculomegaly, periventricular echogenicity, growth restriction and ascites; fetal MRI can add information.
- Sample the amniotic fluid: CMV PCR is done after about 21 weeks and at least six weeks after maternal infection; an early negative result does not exclude fetal infection.
- Counsel on outcome: Explain that most infected infants are well at birth, while symptomatic infection and hearing loss carry prognostic implications.
- Plan the newborn: Arrange hearing screening and a saliva or urine CMV PCR in the first weeks of life, with treatment decisions for symptomatic infants.
Where the examiner tries to catch you
Examiners test the primary versus non-primary distinction and the newborn plan.
- Trap: Counselling on an isolated positive IgM Correct: Avidity testing and fetal ultrasound are needed before any prognostic counselling, because IgM can persist.
- Trap: Assuming a seropositive woman cannot transmit CMV Correct: Non-primary infection can still transmit, though much less often than primary infection.
- Trap: Prescribing valganciclovir to prevent fetal infection Correct: Valganciclovir is avoided in pregnancy, and prevention rests on hygiene and counselling about contact with saliva and urine.
Frequently asked questions
Why is primary CMV infection more dangerous to the fetus than recurrent infection?
Primary CMV infection carries a much higher risk of transmission to the fetus, and severe fetal disease is more likely when maternal infection occurs early in pregnancy. Non-primary infection, from reactivation or reinfection, transmits far less often.
Which sonographic findings suggest congenital CMV?
Growth restriction, ventriculomegaly, periventricular echogenicity, echogenic bowel, ascites and hepatosplenomegaly suggest congenital CMV. These findings are non-specific, so they prompt PCR testing rather than a definitive diagnosis.
When is amniocentesis done for CMV PCR?
Amniocentesis for CMV PCR is usually performed after about 21 weeks of gestation and at least six weeks after maternal infection. A negative result very early after infection does not exclude fetal infection, so repeat testing may be needed.
How is symptomatic congenital CMV treated in a newborn?
Symptomatic congenital CMV in a newborn is treated with valganciclovir, usually for six months, once the diagnosis is confirmed. Hearing is monitored long term, because hearing loss can appear after the neonatal period even in infants who look well at birth.