10.1 Infections in Pregnancy: CMV, Parvovirus, Varicella, Rubella, Toxoplasmosis, Listeria, GBS & HIV
Key Takeaways
Cytomegalovirus is the most common congenital infection and the leading non-genetic cause of sensorineural hearing loss; prevention relies on hygiene around young children's saliva and urine.
Parvovirus B19 can cause fetal anemia and hydrops, most often when infection occurs before 20 weeks, so an infected pregnant patient needs serial middle cerebral artery Doppler studies for 8–12 weeks.
A varicella-susceptible pregnant patient exposed to chickenpox should receive varicella-zoster immune globulin within 10 days, and maternal varicella is treated with acyclovir.
Intrapartum GBS prophylaxis uses IV penicillin G; cefazolin is used for low-risk penicillin allergy, and clindamycin (if the isolate is susceptible) or vancomycin for high-risk allergy, ideally started at least 4 hours before delivery.
Pregnant people with HIV take ART throughout pregnancy, and those with viral loads above 1,000 copies/mL near delivery receive IV zidovudine and a scheduled cesarean at 38 weeks.
Principles
Maternal infections threaten the pregnancy in three ways: direct fetal infection with anomalies or anemia, preterm birth or loss, and transmission at delivery. Gestational age at infection usually predicts severity: first-trimester infection causes structural damage, while later infection causes growth, neurologic, or hematologic effects.
TORCH and Viral Infections
| Infection | Transmission and Risk | Fetal or Neonatal Effects | Key Management |
|---|---|---|---|
| Cytomegalovirus (CMV) | Saliva and urine of young children; transmission about 30%–40% after primary maternal infection, much lower after reactivation | Most common congenital infection; sensorineural hearing loss, microcephaly, periventricular calcifications, chorioretinitis, FGR | No routine screening (ACOG). Diagnose with IgM plus low IgG avidity. Amniotic fluid PCR at least 6 weeks after infection and after 21 weeks. High-dose valacyclovir for primary first-trimester infection reduced transmission in a trial; discuss with maternal-fetal medicine |
| Parvovirus B19 | Respiratory droplets; teachers and parents of young children at risk; transmission about 30% | Suppresses fetal red-cell production → anemia and nonimmune hydrops, highest risk before 20 weeks | IgM/IgG serology after exposure. If acute infection: MCA peak systolic velocity Doppler every 1–2 weeks for 8–12 weeks; intrauterine transfusion for severe anemia |
| Varicella | Highly contagious; maternal pneumonia can be severe | Congenital varicella syndrome (about 2% if infection before 20 weeks): limb hypoplasia, cicatricial skin scars, eye and CNS defects; neonatal varicella if the maternal rash appears from 5 days before to 2 days after delivery | Exposed susceptible patient: VariZIG within 10 days. Maternal infection: oral acyclovir (IV for pneumonia). Newborn gets VariZIG when maternal rash timing is high risk |
| Rubella | Respiratory; rare in the United States because of vaccination | Congenital rubella syndrome: deafness, cataracts, heart defects (PDA, pulmonary stenosis); risk up to 90% with infection before 11 weeks | Check immunity at the first visit; give MMR postpartum, never during pregnancy |
| Toxoplasmosis | Undercooked meat, cat feces, unwashed produce | Chorioretinitis, hydrocephalus, intracranial calcifications | Spiramycin to reduce transmission; pyrimethamine, sulfadiazine, and folinic acid if fetal infection is confirmed |
| Measles | Airborne; outbreaks resurged in 2025 | Miscarriage, preterm birth, low birth weight; severe maternal pneumonia | Susceptible pregnant contacts receive IV immune globulin within 6 days of exposure; MMR postpartum |
| Influenza and COVID-19 | Respiratory | Pregnancy raises risk of severe illness, preterm birth | Vaccinate in any trimester (ACOG); treat influenza promptly with oseltamivir regardless of vaccination status or symptom duration |
| Zika virus | Mosquito bite and sexual transmission | Microcephaly and brain anomalies | Avoid travel to areas with active outbreaks; condom use with exposed partners |
Prevention counseling for every pregnant patient: wash hands after diaper changes and wiping a child's nose and mouth, don't share utensils or kiss young children on the mouth (CMV), avoid cleaning cat litter and wear gloves in soil (toxoplasmosis), cook meat thoroughly, and avoid unpasteurized dairy and cold deli meats (listeria).
Listeriosis
Listeria monocytogenes comes from unpasteurized dairy, soft cheeses, deli meats, and smoked seafood. Pregnant people are about 10 times more likely to be infected. Maternal illness is often a mild flu-like fever with myalgias, but infection can cause miscarriage, preterm labor, stillbirth, and neonatal sepsis or meningitis. Diagnose with blood cultures in a febrile pregnant patient with exposure, and treat with IV ampicillin (with or without gentamicin). Cephalosporins are not effective against Listeria.
Group B Streptococcus (GBS)
- Screening: Rectovaginal culture at 36 0/7–37 6/7 weeks (ACOG 2020) for everyone except those already needing prophylaxis.
- Intrapartum antibiotic prophylaxis (IAP) is indicated for: a positive culture this pregnancy; GBS bacteriuria at any count during this pregnancy; a prior infant with invasive GBS disease; or unknown status with labor before 37 weeks, rupture of membranes for 18 hours or more, intrapartum fever of 100.4 °F (38 °C) or higher, or a positive intrapartum NAAT.
- Not needed: a planned cesarean before labor with intact membranes, even if GBS-positive.
| Situation | Regimen |
|---|---|
| No penicillin allergy | Penicillin G 5 million units IV, then 2.5–3 million units every 4 hours until delivery (ampicillin 2 g IV, then 1 g every 4 hours, is an alternative) |
| Low-risk allergy (no anaphylaxis, angioedema, respiratory distress, or urticaria) | Cefazolin 2 g IV, then 1 g every 8 hours |
| High-risk allergy | Clindamycin 900 mg IV every 8 hours only if the isolate is susceptible; otherwise vancomycin |
Prophylaxis is considered adequate when a beta-lactam is started at least 4 hours before delivery. Penicillin allergy testing during pregnancy helps many patients safely receive first-line therapy.
HIV in Pregnancy
- Start or continue antiretroviral therapy (ART) for every pregnant person regardless of CD4 count, aiming for an undetectable viral load; check viral load around 34–36 weeks to plan delivery.
- Viral load >1,000 copies/mL (or unknown) near delivery: IV zidovudine during labor and a scheduled cesarean at 38 weeks before labor or membrane rupture.
- Suppressed viral load: Vaginal birth is appropriate, and IV zidovudine is not required.
- The newborn receives antiretroviral prophylaxis. Since 2023, federal perinatal guidelines support shared decision-making about breastfeeding for people with sustained viral suppression on ART; replacement feeding eliminates postnatal transmission.
- With treatment, perinatal transmission is below 1%, compared with about 25% without intervention.
Hepatitis B and C in Pregnancy
Screen for HBsAg and HCV antibody in every pregnancy. For HBsAg-positive patients, check HBV DNA; tenofovir starting at 28–32 weeks is recommended when HBV DNA exceeds 200,000 IU/mL, and every newborn of an HBsAg-positive mother receives HBIG plus hepatitis B vaccine within 12 hours. Hepatitis C is treated postpartum; avoid invasive fetal procedures when possible, and breastfeeding is encouraged unless nipples are cracked and bleeding.
A 25-year-old elementary-school teacher at 16 weeks of gestation reports that several students have 'slapped cheek' rashes. Her parvovirus B19 serology shows positive IgM and positive IgG. What is the most appropriate management?
Recommend termination because congenital parvovirus infection causes limb reduction defects.
Give the MMR vaccine now to boost her immunity and prevent transmission to the fetus.
Reassure her that parvovirus B19 does not cross the placenta or affect the fetus.
Begin serial middle cerebral artery Doppler every 1–2 weeks for 8–12 weeks to detect fetal anemia.
A pregnant patient at 39 weeks in active labor had a GBS-positive rectovaginal culture at 36 weeks. She reports that penicillin caused a mild, nonurticarial rash in childhood, with no hives, angioedema, or breathing difficulty. Which intrapartum prophylaxis is most appropriate?
Cefazolin 2 g IV, then 1 g IV every 8 hours until delivery
Vancomycin 20 mg/kg IV every 8 hours
No prophylaxis, because a penicillin allergy excludes GBS treatment
Oral amoxicillin 500 mg every 8 hours
A 30-year-old at 22 weeks of gestation has never had chickenpox or the varicella vaccine, and her varicella IgG is negative. Four days ago she spent an afternoon with a nephew who now has chickenpox. She has no symptoms. What is the most appropriate next step?
Give live varicella vaccine today.
Administer varicella-zoster immune globulin (VariZIG) now.
Start valacyclovir for 6 months as suppressive therapy.
No action is needed unless she develops a rash.
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