Influenza virus infection in the second and third trimesters of pregnancy:a clinical and seroepidemiological study

Objective To determine whether maternal influenza virus infection in the se cond and third trimesters of pregnancy results in transplacental transmissi on of infection, maternal auto-antibody production or an increase in compli cations of pregnancy. Design Case-control cohort study. Population Study and control cohorts were derived from 3975 women who were consecutively delivered at two Nottingham teaching hospitals between May 19 93 and July 1994. A complete set of three sera was available for 1659 women . Methods Paired maternal ante- and postnatal sera were screened for a rise i n anti-influenza virus antibody titre by single radial haemolysis and haema gglutination inhibition. Routine obstetric data collected during and after pregnancy were retrieved from the Nottingham obstetric database. Cord sampl es were tested for the presence of IgM anti-influenza antibodies, and postn atal infant sera were tested for the persistence of influenza-virus specifi c IgG. Paired antenatal and postnatal sera were tested against a standard r ange of auto-antigens by immunofluorescence. Main outcome measures Classification of women as having definite serologica l evidence of an influenza virus infection in pregnancy (cases) or as contr ols. Results Intercurrent influenza virus infections were identified in 182/1659 (11.0%) pregnancies. None of 138 cord sera from maternal influenza cases w as positive for influenza A virus specific IgM. IgG anti-influenza antibodi es did not persist in any of 12 infant sera taken at age 6-12 months. Six o f 172 postnatal maternal sera from cases of influenza were positive for aut o-antibodies. In all cases the corresponding antenatal serum was also posit ive for the same auto-antibody. There were no significant differences in pr egnancy outcome measures between cases and controls. Overall, there were si gnificantly more complications of pregnancy in the cases versus the control s, but no single type of complication achieved statistical significance. Conclusions Influenza infection in the second and third trimesters of pregn ancy is a relatively common event. We found no evidence for transplacental transmission of influenza virus or auto-antibody production in pregnancies complicated by influenza infections. There was an increase in the complicat ions of pregnancy in our influenza cohort.