Pregnancy · Infections
Congenital Infections (TORCH) in Pregnancy
Which infections can pass to baby and matter for antenatal action — CMV, toxoplasmosis, parvovirus, listeria, varicella, syphilis, Zika. Hand hygiene + food safety + vaccines reduce risk. SMFM Consult #71 / RCOG.
Last reviewed 2 June 2026
Congenital infection workup
CMV / parvovirus B19 / toxoplasmosis
Pathogen
IgM
IgG
IgG avidity
Pattern
Incomplete serology
Complete IgM, IgG, and (if both positive) IgG avidity testing. Document maternal contacts (under-3 in household, healthcare/childcare worker).
Troubleshooting + common pitfalls
- Pitfall: Diagnosing primary CMV on IgM alone.
Solution: IgM can persist > 12 months after primary infection. Add IgG AVIDITY — low avidity = recent (< ~16 wk); high avidity = remote, no fetal risk in this pregnancy. - Pitfall: Skipping the ≥ 6-week gap before amniocentesis.
Solution: CMV amnio is most sensitive when done ≥ 21 wk AND ≥ 6 wk after maternal infection. Earlier = false negatives because virus needs time to reach amniotic fluid via fetal kidney. - Pitfall: Not offering valaciclovir for confirmed primary CMV.
Solution: Hughes 2020 Lancet showed valaciclovir 8 g/day reduces vertical CMV transmission by ~70 %. Discuss with fetal-medicine; offer if available. - Pitfall: Reassuring for parvovirus without MCA-PSV surveillance.
Solution: Even asymptomatic maternal infection requires serial MCA-PSV every 1–2 weeks for 8–12 weeks post infection to catch fetal anaemia early. IUT is highly effective if caught. - Pitfall: Treating hydrops without checking for spontaneous resolution potential.
Solution: ~30 % of parvovirus-related fetal hydrops resolves spontaneously. IUT is for documented severe anaemia (MCA-PSV ≥ 1.5 MoM with hydrops), not the picture alone. - Pitfall: Confusing toxoplasmosis severity with transmission rate.
Solution: Transmission RISES with GA; SEVERITY FALLS with GA. 1st-trimester infection has low transmission (10–25 %) but severe sequelae in affected fetuses. 3rd-trimester infection has high transmission (60–90 %) but mild or subclinical fetal disease. - Pitfall: Spiramycin started but pyrimethamine/sulfadiazine not escalated when fetal infection confirmed.
Solution: Spiramycin reduces VERTICAL transmission. Once fetal infection is confirmed on amniocentesis, switch to pyrimethamine + sulfadiazine + folinic acid for FETAL TREATMENT — spiramycin alone is insufficient at that point. - Pitfall: Not counselling CMV prevention for seronegative mothers.
Solution: 50 % of seronegative mothers with daily under-3 contact seroconvert. Counsel hygiene: handwashing, no shared utensils, no kissing on mouth/nose, separate towels. Evidence (Adler 2004): ~50 % reduction in seroconversion with these measures. - Pitfall: Routine toxoplasmosis screening in low-prevalence regions.
Solution: French universal screening makes sense at high seroprevalence; the US/UK don’t routinely screen. Test only on indication (exposure, suggestive illness, ultrasound findings, immunocompromise). - Pitfall: Forgetting to counsel re cat litter for toxo.
Solution: Sporulation of oocysts takes 24 h+; same-day cleaning by another household member is safer than letting them mature. Cooking meat to internal 71 °C kills tissue cysts. - Pitfall: Anti-D Ig given for CMV/parvovirus “just in case” after amniocentesis.
Solution: Anti-D is for Rh-negative mothers regardless of indication. Not specific to congenital-infection workup but easy to forget in the rush. - Pitfall: Forgetting neonatal CMV testing for symptomatic newborns.
Solution: Confirm congenital CMV in any newborn with SGA, microcephaly, hepatosplenomegaly, jaundice, thrombocytopenia, hearing loss, or chorioretinitis — urine or saliva PCR within the first 3 weeks of life (after that, can’t distinguish congenital from postnatal).
Educational tool only — not medical advice. SMFM Consult #71 (2024); RCOG SIP 56 (2021); Hughes Lancet 2020; Adler 2004. Workup and treatment by fetal-medicine / infectious-disease teams.
What does this mean?
The three classic congenital infections of pregnancy share a workup pattern (IgM + IgG ± avidity, GA-aware risk, fetal scans, amniocentesis if needed, targeted treatment) but differ in fetal injury pattern and treatment. CMV is the commonest (~1 in 200 newborns infected; SNHL is the major sequela); IgG avidity distinguishes primary from remote infection, valaciclovir reduces transmission ~70 % (Hughes 2020), and hygiene advice for under-3-contacts cuts seroconversion 50 %. Parvovirus B19 causes anaemia → hydrops 9–20 weeks; serial MCA-PSV is the surveillance tool, IUT is rescue, ~30 % of hydrops resolves spontaneously. Toxoplasmosis has the inverted pattern: transmission rises with GA, severity falls with GA. Spiramycin reduces vertical transmission; pyrimethamine–sulfadiazine treats confirmed fetal infection. The single most common pitfall across all three is making the call on IgM alone — IgM persists for many months and confuses recent vs remote infection without avidity testing.
What are TORCH infections?
Infections that can pass from mum to baby in pregnancy and potentially cause harm:
- Toxoplasmosis
- Other (syphilis, varicella, parvovirus, Zika, listeria)
- Rubella
- Cytomegalovirus (CMV)
- Herpes
Modern grouping focuses on infections where antenatal action changes outcomes.
CMV — the commonest
Herpes-family virus; ~50-80% of adults have been infected (often as a child, with no symptoms). ~1 in 200 newborns infected.
Leading non-genetic cause of childhood hearing loss. Primary infection (first time) in pregnancy most concerning.
Prevention — hand hygiene (evidence-based):
- Wash hands after wiping noses, changing nappies, helping young children.
- Don’t share food, drink, utensils with toddlers.
- Don’t kiss young children on mouth (cheek/forehead OK).
- Clean toys / surfaces shared with kids.
Valaciclovir (Hughes 2020 Lancet): reduces vertical transmission ~70% if primary CMV diagnosed.
Toxoplasmosis
Parasite from raw/undercooked meat + cat faeces. ~1 in 5,000 UK.
Risk to baby varies with gestation: earlier infection = lower transmission but more severe.
Prevention:
- Wear gloves when gardening / cleaning cat litter.
- Thoroughly cook meat.
- Wash vegetables.
- Avoid raw / cured meats.
Treatment: spiramycin if confirmed; further triple therapy if fetus infected.
Parvovirus B19 (“slapped cheek”)
Bright red rash in children. School epidemics common.
In pregnancy: highest concern 9-20 weeks — fetal anaemia, hydrops, miscarriage. ~30% transmission; ~3% chance of fetal hydrops/death.
Blood test confirms maternal infection. MCA Doppler ultrasound every 1-2 weeks. Intrauterine transfusion can save fetal life.
Varicella (chickenpox)
Serious if mum NOT immune. Risks by timing:
- 1st trimester: 0.4-2% risk fetal varicella syndrome.
- 2nd-3rd trimester: minimal risk if mum recovers.
- Around delivery (5 days before-2 days after): life-threatening neonatal varicella; VZIG urgent.
Pre-pregnancy vaccination if no immunity. VZIG within 4-10 days of exposure; aciclovir if symptomatic.
Listeria
Rare (~1 in 5,000) but serious. ~20% miscarriage / stillbirth / preterm risk.
High-risk foods to avoid in pregnancy:
- Unpasteurised milk + cheese.
- Soft cheeses (Brie, Camembert, blue).
- Pâté.
- Refrigerated smoked fish / meat (smoked salmon, ham).
- Deli meats.
- Raw sprouts.
Treatment: ampicillin urgent if confirmed. Blood culture if febrile in pregnancy with exposure.
Zika virus
Mosquito-borne. Avoid travel to endemic areas in pregnancy or when trying. If travel essential: DEET, long sleeves, nets.
Sexual transmission also occurs — barrier methods for 3 months after partner travel.
Vaccines in pregnancy
- COVID-19: safe + recommended.
- Flu: NHS-funded; ideally early autumn.
- RSV: from 28+ weeks (NHS programme 2024).
- Pertussis (whooping cough): 16-32 weeks.
- Avoid live vaccines: MMR pre-pregnancy if needed.
Understanding antibody tests
- IgM: rises within days-weeks of NEW infection; can persist >12 months for CMV / parvovirus / toxo (false positives).
- IgG: rises later; lasts years / lifetime; = immune.
- IgG avidity: low = recent (<16 wk); high = remote. Key test for timing.
Different scenarios — congenital infection
Scenario 1: Toddler in childcare; pregnant with second baby
High CMV exposure risk. Hand hygiene crucial. Don’t share food/utensils; cheek/forehead kisses only.
Scenario 2: Garden + outdoor cat; first pregnancy
Wear gloves in garden; let someone else do litter; cook meat thoroughly. Toxoplasmosis testing if symptomatic.
Scenario 3: Slapped cheek epidemic at older child’s school, 16 weeks pregnant
Avoid known cases. Parvovirus B19 IgG / IgM blood test. If exposed + non-immune, surveillance ultrasound 9-20 wk for fetal anaemia.
Scenario 4: Chickenpox exposure, no childhood history
Antibody check. If non-immune: VZIG within 4-10 days. Aciclovir if symptoms develop. Plan delivery timing if around term.
Scenario 5: Unexpected travel to Zika area
Pre-travel: assess necessity; if going, DEET + long clothing. Post-travel: Zika PCR if symptomatic; serial fetal scans for microcephaly. Sexual transmission consideration.
Care guidance — congenital infections
- Routine booking: HIV, HepB, syphilis, rubella immunity.
- CMV prevention: hand hygiene around young children.
- Toxoplasmosis: gloves gardening, cooked meat.
- Listeria: avoid unpasteurised / soft cheeses / pâté.
- Parvovirus: avoid known epidemics 9-20 wk.
- Varicella: VZIG urgent if exposed + non-immune.
- Vaccines: COVID, flu, RSV, pertussis recommended.
- Don’t ignore fever in pregnancy; tell midwife.
- Hand hygiene simple, effective.
Sources
- SMFM Consult #71 (2024). Cytomegalovirus in pregnancy.
- RCOG. Multiple Green-top Guidelines (parvovirus, varicella, syphilis, etc.)
- NICE NG201. Antenatal care.
- Hughes BL, et al. Valaciclovir for primary maternal cytomegalovirus infection: a randomised trial. Lancet 2020.
- UK Travel Health Pro. Zika and pregnancy advice.
- NHS. Foods to avoid in pregnancy.
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Frequently asked questions
What are 'TORCH' infections?
INFECTIONS that can pass from mum to baby in pregnancy and potentially cause harm. CLASSIC TORCH: TOXOPLASMOSIS, OTHER (syphilis, varicella, parvovirus, Zika, listeria etc.), RUBELLA, CYTOMEGALOVIRUS (CMV), HERPES. Modern grouping focuses on infections where ANTENATAL action changes outcomes. KEY ONES: CMV (most common, 1 in 200 newborns infected), TOXOPLASMOSIS (cat litter, undercooked meat), PARVOVIRUS B19 (school epidemics; fetal anaemia 9-20 wk), RUBELLA (rare in vaccinated populations, severe if infected), LISTERIA (foodborne), ZIKA (travel-related). Each has different prevention + management.
How can I get tested?
BOOKING ROUTINE: NHS UK includes — Hepatitis B, HIV, syphilis, rubella IMMUNITY. NOT routine: CMV, toxoplasmosis (some countries do, e.g. France for toxo). PRIVATE TORCH SCREEN: ~£100-300. AVAILABLE if symptoms / risk: respiratory illness with fetal anomaly findings, exposure to known case, immunosuppressed. BLOOD TESTS: IgG (past exposure / immunity) + IgM (recent / acute infection) + sometimes IgG AVIDITY (timing of infection). RESULTS interpreted carefully — false positives common, especially IgM.
What is CMV and why does it matter?
CYTOMEGALOVIRUS (CMV) — herpes family virus; ~50-80% adults have been infected (often as child, no symptoms). PREGNANT WOMEN: PRIMARY infection (first time) most concerning — 1/3 pass to baby; ~10% of infected babies have lasting effects (hearing loss most common — leading NON-genetic cause of childhood hearing loss); some have major problems (microcephaly, learning disability, vision/hearing loss). REINFECTION / REACTIVATION: lower transmission, less severe usually. PREVENTION: HAND HYGIENE (esp. after handling young children's saliva, nappies) — most catch CMV from toddlers in nursery.
Can I prevent CMV?
PARTIAL — HAND HYGIENE is the most evidence-based. HIGH-RISK contact: toddlers, nursery workers, healthcare staff with children. ADVICE (RCOG / ACOG): (1) WASH HANDS thoroughly after wiping noses, changing nappies, helping young children to wash; (2) DON'T share food, drink, utensils with toddlers; (3) DON'T kiss young children on mouth (cheek/forehead OK); (4) Clean toys / surfaces shared with kids. EVIDENCE: hand hygiene reduces CMV seroconversion ~50% (Vauloup-Fellous 2009). VALACICLOVIR (Hughes 2020 Lancet): if primary CMV diagnosed, can reduce vertical transmission ~70%. NEW intervention; not universal yet.
What about toxoplasmosis?
PARASITE found in raw/undercooked meat + cat faeces. ~1 in 5,000 pregnancies (UK lower than France). PRIMARY INFECTION IN PREGNANCY: most adults infected without symptoms (mild flu-like). RISK to baby: depends on GESTATION — 1ST TRIMESTER lower transmission (~5%) but more severe; 3RD TRIMESTER higher transmission (~65%) but milder. SEVERE: hydrocephalus, eye problems (chorioretinitis), brain calcifications, learning disability. PREVENTION: wear gloves when gardening / cleaning cat litter (or get someone else to do it); thoroughly cook meat; wash vegetables; avoid raw / cured meats.
How is toxoplasmosis treated in pregnancy?
IF PRIMARY infection confirmed: SPIRAMYCIN — reduces vertical transmission ~50%. IF FETAL infection confirmed (amniocentesis): combined SPIRAMYCIN + PYRIMETHAMINE + SULFADIAZINE + FOLINIC ACID for remainder of pregnancy. NEONATAL TREATMENT: long-term medication if baby infected at birth. SCREENING: not routine UK; France, Austria do screen routinely. PRIVATE testing: £50-150.
What's parvovirus B19?
Causes 'fifth disease' / 'slapped cheek syndrome' — bright red rash in children. ALSO called 'erythema infectiosum'. ADULTS: usually mild. SCHOOL EPIDEMICS common. IN PREGNANCY: HIGHEST CONCERN at 9-20 WEEKS — can cause fetal anaemia, hydrops fetalis (fluid accumulation), miscarriage. RISK: ~30% transmission if mum gets infected; ~3% chance of fetal hydrops/death if 9-20 weeks. >20 weeks: lower risk. BLOOD TEST confirms maternal infection. ULTRASOUND surveillance every 1-2 weeks (MCA Doppler for anaemia). INTRAUTERINE TRANSFUSION can save fetal life if severe anaemia detected. PREVENTION: avoid exposure to known parvovirus B19 cases during pregnancy.
What about chickenpox in pregnancy?
VARICELLA. SERIOUS if mum NOT immune (most adults immune from childhood). RISK to baby varies with timing: (1) 1ST TRIMESTER: 0.4-2% risk of fetal varicella syndrome (limb abnormalities, eye/brain problems); (2) 2ND-3RD TRIMESTER: minimal fetal risk if mum recovers; (3) AT BIRTH (5 days before-2 days after): NEONATAL VARICELLA — life-threatening; mum must receive immunoglobulin (VZIG) urgently; baby treated post-birth. PREVENTION: pre-pregnancy vaccination if no immunity. EXPOSURE: VZIG within 4-10 days; aciclovir if symptoms develop. PREGNANCY-SPECIFIC respiratory complications more severe.
Is the listeria warning serious?
YES — though rare (~1 in 5,000 pregnancies). LISTERIA MONOCYTOGENES bacteria from contaminated food. HIGH-RISK FOODS: UNPASTEURISED milk + cheese; SOFT CHEESES (Brie, Camembert, blue); pâté; refrigerated smoked fish / meat (smoked salmon, ham); deli meats; raw sprouts; unwashed produce. SYMPTOMS: flu-like, fever, muscle aches, sometimes GI. RISK TO BABY: ~20% miscarriage / stillbirth / preterm birth; neonatal sepsis. TREATMENT: AMPICILLIN urgent. SCREEN: blood culture if febrile in pregnancy with exposure. AVOID risk foods entirely in pregnancy. NHS food safety guide.
What about Zika virus?
MOSQUITO-BORNE virus. EPIDEMIC 2015-2016 South America; ongoing transmission tropical regions. RISK in pregnancy: MICROCEPHALY (small head + brain), EYE problems, congenital Zika syndrome. PREVENTION: AVOID travel to endemic areas during pregnancy / trying; if travel essential — DEET mosquito repellent, long sleeves, treated nets; SEXUAL transmission also occurs — barrier methods for 3 months after partner travel. TESTING: blood + urine PCR in active outbreak areas. CURRENT UK risk LOW; check up-to-date Travel Health advice. NO VACCINE.
What about syphilis screening?
ROUTINE booking blood test in UK (NHS). SYPHILIS IN PREGNANCY: serious — vertical transmission causes congenital syphilis (stillbirth, bone abnormalities, neurological problems, deafness). PREVENTION: PENICILLIN injections — highly effective if treated by 32 wk. SCREENING also at risk events (multiple partners, etc.). NOT a moral judgment — universal NHS screening. RATES RISING in UK + globally; vigilance maintained.
What if I have an unusual fever / illness in pregnancy?
DON'T IGNORE. Causes: (1) Common viral (cold, flu); (2) UTI / kidney infection; (3) RESPIRATORY infection (COVID, RSV, flu); (4) GI (food poisoning, listeria, CMV); (5) Specific exposures (parvovirus, varicella, toxo). RED FLAGS: high fever (>38.5°C); severe headache; rash; confusion; severe abdominal pain; reduced fetal movements; respiratory difficulty. SEE GP / midwife / hospital. TELL them you're pregnant. APPROPRIATE testing + treatment urgent.
Can I get COVID / RSV / flu vaccines in pregnancy?
(1) COVID-19: SAFE + RECOMMENDED in pregnancy; reduces severe maternal illness + neonatal protection via antibodies. ANY trimester. (2) FLU: NHS-funded; SAFE + RECOMMENDED; ideally early autumn. (3) RSV: NEW NHS programme 2024 — pregnant women 28+ wk offered to protect baby first 6 months. SAFE. (4) PERTUSSIS (whooping cough): NHS from 16-32 weeks; protects baby first few months. ALL vaccines RECOMMENDED — protect mum + baby. AVOID: live vaccines (MMR — give pre-pregnancy if needed; yellow fever — avoid travel).
What's the difference between IgG, IgM, and IgG avidity?
ANTIBODIES — your immune response to infection. IgM: rises within DAYS-WEEKS of NEW infection; fades over months. POSITIVE = recent? But: false positives common; can persist >12 months for CMV / parvovirus / toxo. IgG: rises LATER, lasts YEARS / LIFETIME. POSITIVE = immune (past infection or vaccination). IgG AVIDITY: how 'mature' the antibody is. LOW AVIDITY = recent infection (<16 weeks ago); HIGH AVIDITY = remote infection. KEY TEST for distinguishing recent vs old infection — especially useful in CMV / toxo.
How does this relate to other calculators on BumpBites?
Companion: /calculators/pregnancy-food-safety for listeria avoidance; /calculators/vaccine-scheduler for routine pregnancy vaccines; /calculators/anti-d-dosing (parvovirus B19 link to anaemia); /calculators/fetal-weight if growth concerns; /calculators/preeclampsia-diagnosis; /calculators/icp-cholestasis (liver overlap).