Subclinical rubella in pregnancy--occurrence and outcome

Between the years 1972 and 1979, 40,589 pregnant women were tested for rubella antibodies following suspected illness or exposure, using hemagglutination-inhibition (HI), complement fixation and staphylococcal absorption for determination of specific immunoglobulin M (IgM). Recent primary infection was confirmed by antibody rise in paired sera and/or the presence of specific IgM. Reinfection was differentiated from primary asymptomatic rubella by absence of specific IgM. Determination of neutralizing antibodies was also useful in confirming reinfections. Clinical rubella was confirmed in 1,448 patients (3.6%). In 154 cases asymptomatic rubella infection was detected; 98 had primary infection and 56 experienced reinfection. In a selected group of 2,200 women exposed to confirmed rubella, 6.8% had clinical rubella, 3.8% asymptomatic infection, and in 7.1% the results were doubtful. Reinfection was detected in 12.4% of 265 women with initially low HI titers. The prospective follow-up on pregnancy outcome was available in 87 women with asymptomatic infection. Seven cases of congenital rubella were detected in the group of primary infections, while all 25 children born following reinfection were healthy.