Infections, such as cytomegalovirus (CMV), Zika, HIV, hepatitis B and C, skin infections, and lower respiratory tract infections
Description
- Multiple unrelated organisms grouped by a shared problem: maternal infection with a distinct risk to the fetus/neonate
- Two transmission patterns
- Vertical (transplacental/perinatal) - CMV, Zika, HIV, hepatitis B/C, varicella, parvovirus B19
- Maternal severity amplified by pregnancy - influenza, pneumonia (physiological dec FRC + immune shift -> more severe LRTI)
- CMV is the commonest congenital infection worldwide
Epidemiology
- CMV - seroprevalence ~50-60% adults; primary infection in ~1-4% of seronegative pregnant women; congenital CMV ~0.5-1% of all births
- HIV - Australia has low prevalence; universal antenatal screening detects most cases
- Hepatitis B - higher prevalence in migrants from endemic regions (Asia-Pacific, sub-Saharan Africa) and some Aboriginal and Torres Strait Islander communities
- Hepatitis C - associated with injecting drug use history
- Zika - travel-related in Australia (no local transmission) - relevant to travel history in pregnancy
- Varicella - most adults immune (past infection/vaccination); non-immune exposure in pregnancy is the concern
- Influenza/pertussis - vaccine-preventable, both recommended in every pregnancy
Aetiopathogenesis
Mechanisms of fetal harm by organism
| Organism | Highest-risk window | Mechanism/effect |
|---|---|---|
| CMV | Any trimester (primary infection > reactivation) | Transplacental; SNHL, microcephaly, chorioretinitis |
| Zika | 1st trimester | Neurotropic - microcephaly, brain calcification |
| HIV | Intrapartum > antepartum | Blood/genital secretion exposure; risk proportional to maternal viral load |
| Hepatitis B | Intrapartum (mainly) | Blood exposure at birth; risk correlates with maternal HBV DNA and HBeAg status |
| Hepatitis C | Intrapartum | Blood exposure; risk inc with HIV co-infection |
| Varicella | <20 weeks (congenital varicella syndrome); peripartum (5 days before to 2 days after birth) = severe neonatal varicella | Transplacental / direct neonatal exposure without passive antibody |
| Parvovirus B19 | <20 weeks | Suppresses fetal erythropoiesis -> anaemia, hydrops fetalis |
- Physiological pregnancy immune shift (Th2-skewed) + reduced FRC -> influenza and pneumonia cause disproportionately severe maternal illness
Diagnosis
Universal antenatal screening (booking bloods)
- HIV, hepatitis B surface antigen, syphilis - offered to all
- Hepatitis C - screened if risk factors (or universally per local protocol)
- Rubella and varicella immunity checked; CMV not routinely screened
By organism
- CMV - maternal IgM/IgG +/- avidity (low avidity = recent infection); amniocentesis PCR >=6 weeks after presumed infection and >=21 weeks gestation for fetal infection; serial growth/neuro ultrasound
- Zika - travel history is the trigger; serology/PCR per travel exposure, referral to specialist service
- HIV - confirm with repeat serology; baseline viral load, CD4, resistance testing
- Hepatitis B - HBsAg positive -> HBV DNA viral load + HBeAg to stratify transmission risk and need for antiviral prophylaxis
- Hepatitis C - HCV RNA if antibody positive (confirms active infection)
- Varicella exposure in a non-immune woman - check varicella IgG urgently (many report uncertain history are actually immune)
Management
CMV
- No vaccine; hyperimmune globulin no longer recommended for secondary prevention (superseded by valaciclovir evidence)
- Primary infection <1st half of pregnancy - high-dose valaciclovir (8 g/day) reduces vertical transmission
- Confirmed fetal infection - consider continuing valaciclovir after specialist discussion; neonatal valganciclovir if symptomatic congenital CMV
Zika
- No treatment - supportive; avoid travel to endemic areas in pregnancy where possible
- Confirmed exposure -> serial fetal neuro-imaging
HIV
- Combination ART for all, started as early as possible, target undetectable viral load
- Viral load >=1000 copies/mL (or unknown) near term -> IV zidovudine intrapartum + consider elective caesarean at 38 weeks
- Viral load undetectable at term - vaginal birth reasonable, avoid unnecessary instrumentation/fetal scalp electrode
- Avoid breastfeeding where safe formula feeding is available (in resource-rich settings including Australia)
- Neonate: ART prophylaxis 2-6 weeks depending on maternal viral suppression
Hepatitis B
- Maternal HBV DNA >200,000 IU/mL (~5.3 log10) -> tenofovir from ~28-32 weeks to 4 weeks postpartum - reduces breakthrough transmission despite neonatal immunoprophylaxis
- All neonates of HBsAg+ mothers: hepatitis B immunoglobulin + vaccine within 12h of birth, then complete schedule
- Breastfeeding safe once neonate immunised
Hepatitis C
- No effective intervention to reduce vertical transmission in pregnancy (DAAs not used antenatally - limited safety data)
- Avoid invasive procedures (fetal scalp electrode, prolonged rupture of membranes) where possible
- Breastfeeding not contraindicated unless nipples cracked/bleeding
- Infant testing for HCV RNA/antibody after 18 months
Varicella
- Non-immune + significant exposure -> VZIG within 96h (up to 10 days)
- Maternal chickenpox in pregnancy -> oral valaciclovir/aciclovir if presents within 24h of rash, especially >20 weeks
- Peripartum maternal varicella (5 days before to 2 days after birth) -> neonate needs VZIG +/- aciclovir - high risk of severe neonatal varicella
- Avoid live varicella vaccine in pregnancy (give postpartum if non-immune)
Influenza / LRTI
- Inactivated influenza vaccine recommended in every pregnancy, any trimester
- Pertussis vaccine (dTpa) recommended 20-32 weeks each pregnancy - passive neonatal protection
- Treat maternal pneumonia promptly and admit early - lower threshold than non-pregnant given reduced respiratory reserve
- Oseltamivir for confirmed/suspected influenza - safe in pregnancy, most benefit if started within 48h
Associations
- CMV - sensorineural hearing loss (may be delayed-onset), microcephaly, chorioretinitis, hepatosplenomegaly, petechiae
- Zika - microcephaly, brain calcifications, arthrogryposis
- Congenital varicella syndrome - limb hypoplasia, cutaneous scarring, eye defects
- Parvovirus B19 - fetal anaemia, hydrops, (rarely) fetal loss
- HIV/HBV/HCV - primarily perinatal transmission risk rather than structural malformation
Natural history & complications
- CMV - majority of congenitally infected infants are asymptomatic at birth, but ~10-15% of these develop delayed sensorineural hearing loss
- HIV/HBV/HCV with appropriate perinatal intervention - vertical transmission risk reduced to <1-2%
- Varicella/parvovirus - risk highest with early pregnancy infection, but overall fetal risk from a single exposure is modest
- Vaccination (influenza, pertussis, and pre-pregnancy varicella/rubella/hepatitis B where indicated) is the most effective preventive strategy across this group
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