The rubella virus is one of a small number of infectious agents that can cross the placenta and infect the developing embryo. The virus can cause a generalised and persistent foetal infection that is still present in the newborn.
By mechanisms that are poorly understood, the virus is particularly damaging to the eye and heart during critical periods of their development and can cause severe structural defects such as microphthalmos and ventricular septal defects. Other structures are damaged by tissue destruction and scarring resulting in hearing loss, cataracts, brain damage, chorioretinopathy and pulmonary artery stenosis.
It is important to understand that the effect of rubella on prenatal development depends upon the stage of pregnancy at which the infection occurs. Although the precise risk is not known there appears to be up to an 80% chance of foetal damage after infection in the first 8 weeks of gestation (post fertilisation), this decreases to about 30% for weeks 9 to 12 and 17% for weeks 13 to 16. Defects are rare when infection occurs after 16 weeks gestation.
Sensorineural hearing loss (deafness) is the most common of all rubella associated defects and may be the only defect in an affected child. It can result from infection at any time during the first 4 months of gestation although the highest risk is from early infection. Mental retardation (IQ score below 70) is the next most frequent defect followed by cardiac defects, particularly persistent ductus arteriosus and pulmonary artery stenosis. Additionally, the virus may remain in the tissues of the neonate and may continue to cause pathology including diabetes mellitus due to long term chronic viropathy in the islets of Langerhans of the pancreas.
For details on development of the foetal immune response and its limited ability to control the rubella virus late in gestation refer to the references.
Hanshaw JB, Dudgeon JA, Marshall WC, eds. Rubella. In: Viral Diseases of the Fetus and Newborn. 1985 - For general information on the clinical aspects of rubella infection in pregnancy refer to either of these sources
Banatvala JE, Best JM. Rubella. In: Topley & Wilson's Principles of bacteriology, virology and immunity / general editors, M.T. Parker, L.H. Collier. London ; Melbourne : Edward Arnold, c1990. (8th Ed.), 502-27 - For general information on the clinical aspects of rubella infection in pregnancy refer to either of these sources
South MA, Sever JL. Teratogen Update: The congenital rubella syndrome. Teratology 1985; 31(2): 297-307 - For details and discussion on pathogenesis and foetal immune response
Forrest J, Turnbull F, Sholler G, Hawker R, Martin F, Doran T, Burgess, M. Gregg's congenital rubella patients 60 years later. Medical Journal Of Australia. 2002; 177(11/12):664-667 - For further information on rubella