TORCH Infections in Pregnancy
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Direct answer
TORCH is a mnemonic for congenital infections that cross the placenta, namely toxoplasmosis, rubella, cytomegalovirus and herpes simplex, with syphilis, varicella, parvovirus B19 and HIV often added. Each organism produces a characteristic set of fetal defects, and the risk depends on the timing of maternal infection. Screening is targeted to clinical history and serology rather than performed as a universal panel for every pregnant woman.
What you must remember
- Toxoplasmosis: Hydrocephalus, intracranial calcification and chorioretinitis form the classic triad; acquired from undercooked meat or cat faeces.
- Rubella: Cataract, sensorineural deafness and patent ductus arteriosus form the classic triad of congenital rubella syndrome.
- Cytomegalovirus: The commonest congenital infection, with microcephaly, periventricular calcification, hepatosplenomegaly, petechiae and sensorineural hearing loss.
- Herpes simplex: Congenital infection is rare; most neonatal herpes is acquired at delivery from genital lesions and causes skin, eye and mouth disease or encephalitis.
- Varicella: Limb hypoplasia, dermatomal scarring, Horner syndrome and cortical atrophy form the congenital varicella syndrome.
- Parvovirus B19: Fetal anaemia leading to hydrops and fetal death, especially when infection occurs before about 20 weeks.
- Syphilis: Hepatosplenomegaly, rash, rhinitis and bone changes are the early features; the Hutchinson triad is the late picture.
Organism, timing and fetal features
The table lists the gestation at which fetal harm is most likely and the features an examiner expects in a vignette. Learn the timing and the features together.
| Organism | Timing of highest fetal risk | Classic fetal features |
|---|---|---|
| Toxoplasmosis | Severity highest with first-trimester infection | Hydrocephalus, intracranial calcification, chorioretinitis |
| Rubella | First trimester, falling after about 20 weeks | Cataract, deafness, patent ductus arteriosus |
| Cytomegalovirus | Primary infection at any gestation, most severe when early | Microcephaly, periventricular calcification, hearing loss |
| Herpes simplex | Near delivery, for neonatal rather than congenital disease | Skin vesicles, chorioretinitis, encephalitis |
| Parvovirus B19 | Before about 20 weeks, for hydrops | Anaemia, hydrops, intrauterine death |
Rubella causes the most severe defects in early pregnancy, congenital varicella syndrome is mainly seen with infection at about 13 to 20 weeks, while CMV and toxoplasmosis transmit more often later in pregnancy. Use the table to link a fetal scan finding with the likely organism, not as a complete diagnostic list.
Screening is targeted rather than universal. Rubella immunity is checked at booking in many settings, toxoplasmosis and CMV serology are sent when history or ultrasound suggests infection, and HSV status is assessed near term.
Where the examiner tries to catch you
The traps here are about panels, calcification patterns and neonatal herpes.
- Trap: Ordering a full TORCH panel for every pregnant woman Correct: Targeted serology guided by history and scan findings is the approach, because universal panels produce uninterpretable IgM results.
- Trap: Attributing neonatal herpes to congenital transmission Correct: Most neonatal herpes is acquired during passage through an infected birth canal, and caesarean is considered for active genital lesions near delivery.
- Trap: Calling every intracranial calcification CMV Correct: CMV calcifications are periventricular, whereas toxoplasmosis calcifications are scattered, usually with chorioretinitis and hydrocephalus.
Frequently asked questions
What is the classic triad of congenital toxoplasmosis?
Congenital toxoplasmosis classically presents with hydrocephalus or ventriculomegaly, intracranial calcification and chorioretinitis. Hepatosplenomegaly and anaemia may also be seen in neonates, and sequelae can appear later in childhood.
Why is universal TORCH screening not recommended?
Universal TORCH screening is not recommended because results are often uninterpretable without the clinical history, and IgM can be falsely positive. Serology is requested selectively when history or ultrasound suggests infection, and IgG avidity helps interpret the result.
When is amniotic fluid PCR used in suspected fetal TORCH infection?
Amniotic fluid PCR is used to confirm fetal toxoplasmosis and cytomegalovirus infection, with timing set by the organism. Toxoplasmosis PCR is generally done after 18 weeks, and CMV PCR after about 21 weeks, at least several weeks after maternal infection.
Which TORCH infection causes a blueberry muffin rash?
Congenital cytomegalovirus and rubella are both associated with a blueberry muffin rash, caused by extramedullary haematopoiesis and thrombocytopenia. In a vignette, CMV is more likely if periventricular calcification and microcephaly are also described.