Abstract
There is a combination of age groups with low rubella antibody titers due to the complex rubella vaccination schedule prior to 1995. These complicated titers make serologic interpretation difficult. We analyzed fluctuations in the hemagglutinin inhibition of the rubella virus（RV-HI）and RV-IgM titers in pregnant women between January 2015 and August 2021. We then investigated the interpretation of serology and perinatal outcomes. Rubella infection could not be excluded in 345 patients according to serological testing, symptoms, or medical history. The 345 patients were classified into 4 groups: Group I, rubella HI ratio <4×, IgM antibody-negative; Group II, rubella HI ratio <4×, IgM antibody-positive; Group III, rubella HI ratio 4×, IgM antibody-negative; and Group IV, rubella HI ratio 4×, IgM antibody-positive or positive conversion. Group I included 297 patients （86.1%）without rubella infection. In Group II, 43 patients（12.5%）were diagnosed with persistent IgM. Among Groups II to IV, the possibility of infection could not be ruled out in seven cases, four of which required invasive tests. Three patients were polymerase chain reaction（PCR）-negative and were determined to have a high antibody titer due to the booster effect, while one patient was PCR-positive and was diagnosed with congenital rubella syndrome.
