CMV in pregnancy

Background

• Infection with cytomegalovirus during pregnancy
• Infection can be primary infection, non-primary reinfection with another strain, or non-primary reactivation of latent virus
• Mainly of concern because of the risk of causing congenital CMV

Epidemiology

• Maternal seroconversion in about 2% of pregnancies
  • Higher in childcare workers
• Risk of transmission to fetus
  • About 1 in 200 live births in US
  • Primary infection: 30% risk of congenital CMV; higher risk later in pregnancy, but worse outcomes earlier
  • Non-primary
    • Reinfection: 5% risk
    • Reactivation: 1% risk

Diagnosis

• Serology with IgM and IgG
  • IgM usually positive for 6 weeks after primary infection, but can remain positive for as long as 12 months
  • IgM has false positives, including from rheumatoid factor, EBV infection, lupus

IgG	IgM	Avidity	Interpretation
+	–	N/A	past infection, low risk for congenital infection
+	+	high	past infection, low risk for congenital infection
+	+	low	primary maternal infection within the past 3 months
–	–	N/A	either no infection, or repeat in 4 weeks

• Fetal infection is confirmed by amniocentesis sent for PCR
  • To minimized the risk of a false-negative result, it should be be done after 17 weeks gestation and at least 7 weeks after maternal infection

Management

• Counsel mother on risk of fetal infection and subsequent development of congenital CMV
• If they would terminate if CMV-positive due to those risks, then proceed with amniocentesis to diagnose