Embryology · Teratology and prenatal diagnosis
TORCH infections: what each agent does to the embryo and fetus !
- Teratogen
Maternal infections that cross the placenta or pass during birth and can harm the baby's brain, eyes, ears and heart.
Updated 2026-11-01
See it in 3D: Retina · Cochlea · Lens · Lateral ventricles · Liver
What it is
TORCH groups the agents that infect the embryo or fetus: toxoplasma, 'other' (syphilis, varicella, parvovirus B19, Zika, Listeria), rubella, cytomegalovirus and herpes simplex. They share signs at birth, but each has classic findings that point to the diagnosis. Early infection tends to cause malformations; late infection tends to cause active neonatal infection.
Key facts
- Shared signs: growth restriction, hepatosplenomegaly, jaundice, petechiae and thrombocytopenia.
- Many infected newborns have no symptoms at birth and develop deafness or visual problems later.
- Congenital varicella: dermatomal skin scars, limb hypoplasia and eye lesions; risk highest between weeks 13 and 20.
- Parvovirus B19: infects red cell precursors and causes severe fetal anaemia and hydrops.
- Zika: severe microcephaly with subcortical calcifications and macular lesions.
Critical period and mechanism
- Most arrive across the placenta after a primary maternal infection; herpes simplex is mainly passed in the birth canal.
- First trimester: infection disrupts organogenesis and causes malformations (rubella, varicella, severe toxoplasmosis).
- Later: active infection of the fetus or newborn predominates (hepatitis, encephalitis, sepsis).
- Mechanisms: death of progenitor cells, inflammation with calcification, and vascular damage.
Prevention
- Rubella and varicella vaccination before pregnancy (live vaccines, not given during pregnancy).
- Toxoplasma: avoiding undercooked meat and contact with cat faeces or contaminated soil.
- CMV: hand hygiene after contact with young children's saliva or urine, and not sharing utensils.
- Syphilis screening and treatment in prenatal care; protection from mosquito bites (Zika).
TORCH agent and classic findings
| Agent | Classic findings |
|---|---|
| Toxoplasma gondii (toxoplasma_gondii) | Chorioretinitis, hydrocephalus, diffuse calcifications |
| Treponema pallidum (treponema_pallidum) | Rhinitis, palm-and-sole rash; later Hutchinson teeth, saddle nose |
| Rubella virus (rubella_virus) | Cataracts, deafness, patent ductus arteriosus |
| Cytomegalovirus (cmv) | Microcephaly, periventricular calcifications, deafness |
| Herpes simplex (hsv_2, hsv_1) | Vesicles, encephalitis, disseminated disease |
| Varicella-zoster (varicella_zoster_virus) | Dermatomal scars, limb hypoplasia |
| Parvovirus B19 (parvovirus_b19) | Severe fetal anaemia, hydrops |
| Zika virus (zika_virus) | Severe microcephaly, subcortical calcifications, arthrogryposis |
| Listeria monocytogenes (listeria_monocytogenes) | Miscarriage, preterm birth, neonatal sepsis and meningitis |
What it does to the embryo and fetus
- At birth: growth restriction, microcephaly, hepatosplenomegaly, jaundice, petechiae or a 'blueberry muffin' rash.
- Eyes: chorioretinitis (toxoplasma, CMV), cataracts (rubella), macular scars (Zika).
- Ears: sensorineural deafness, mainly from CMV and rubella; it can appear months later.
- Fetal death, miscarriage or hydrops (parvovirus B19, syphilis).
Test yourself
Think of the answer, then tap the question to see it.
Which congenital infection is the leading non-genetic cause of sensorineural deafness?
Cytomegalovirus.
Which triad suggests congenital toxoplasmosis?
Chorioretinitis, hydrocephalus and diffuse intracranial calcifications.
Which late findings make up the Hutchinson triad of congenital syphilis?
Hutchinson teeth (notched, peg-shaped incisors), interstitial keratitis and sensorineural deafness.
Why does parvovirus B19 cause fetal hydrops?
It infects erythroid precursors and causes severe fetal anaemia, leading to heart failure and generalized oedema.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Congenital rubella syndrome
- Congenital Zika syndrome
- Microcephaly
- Congenital hydrocephalus: aqueductal stenosis
- Coloboma, congenital cataract and congenital glaucoma
- Congenital hearing loss, microtia and preauricular pits
- Placenta: structure, circulation and functions
- Principles of teratology: critical periods, dose and genotype
Related conditions
- Congenital (TORCH) infections: syphilis, toxoplasmosis, CMV and Zika
- Syphilis
- Varicella (chickenpox)
- Genital herpes (herpes simplex infection)
- Hearing loss (conductive and sensorineural, including sudden hearing loss)
- Cataract
- Zika virus infection
- Neonatal sepsis
Microorganisms
- Toxoplasma gondii
- Treponema pallidum
- Rubella virus
- Cytomegalovirus
- Herpes simplex virus 2
- Herpes simplex virus 1
- Varicella-zoster virus
- Zika virus
- Parvovirus B19
- Listeria monocytogenes
Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.
Sources: Embryology, Teratology TORCH (StatPearls Publishing (NCBI Bookshelf), 2023); CMV in Newborns (CDC, 2024); Pregnancy and Rubella (CDC, 2024); Congenital Zika Syndrome (CDC, NCBDDD (archived surveillance manual), 2020).
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Representative model, for educational purposes only.