Is pregnancy immunosuppressive? Humoral immunity against viruses

Serum samples were obtained during the first trimester, second trimester, third trimester, at delivery and 6 weeks postpartum from each of 50 pregnant women. All 250 sera were tested for their content of antibodies specific for herpes simplex, measles, rubella and influenza A viruses. The geometric mean titres of antiviral antibody were shown to decline by 18-48% between the times of booking and delivery, and to return to initial values by the end of the puerperium. By means of two-way analysis of variance, the major confounding variable of differences between individuals was identified and controlled for, so that the progression of pregnancy was shown significantly to decrease titres of antiviral antibody. After allowance was made for haemodilution, antibody levels against two viruses (herpes simplex, measles) still declined significantly while those for rubella and influenza viruses actually increased significantly, so that no consistent effect of pregnancy was demonstrable. We conclude that the declining titres of antiviral antibodies seen in pregnant women are predominantly a manifestation of haemodilution and discuss the reasons for believing that humoral immunity remains intact during pregnancy.