691: Do pregnant women have lower than expected measles antibody titers?

Abstract

Though measles vaccination is thought to confer lifelong immunity, antibody titers obtained during routine prenatal screening are sometimes found to be below the threshold for immunity. The altered physiology of pregnancy is a possible explanation for this phenomenon in previously immunized women. The objective of this study was to determine whether titers were more often below the threshold for immunity in pregnant women than would otherwise be expected for their age. A 1:1 matched case-control study comparing measles IgG titers of nulliparous pregnant and non-pregnant women was performed. Titers from pregnant women were obtained from prenatal records of a major academic teaching hospital and titers from non-pregnant women were obtained from local screening programs. All labs used similar IgG cutoffs as a threshold for immunity. Previously vaccinated, nulliparous women aged 15-49 with no history of recent vaccination (within 28 days) were included in the analyses. Wilcoxon signed-rank test was used to compare titers above and below the threshold for immunity between age-matched pregnant and non-pregnant women. 133 pregnant women matched to 133 non-pregnant women by exact age were compared. The mean age was 29.1 years (± 6.2 years). Measles IgG titers were above the threshold for immunity in 87.2% of pregnant women and in 81.2% of non-pregnant women, which was not a significant difference (p=0.24) (Figure). In this cohort of previously vaccinated, nulliparous women, pregnant women were as likely to have measles titers below the threshold for immunity than their age-matched, non-pregnant peers. This suggests that pregnancy is not associated with falsely low titers. Further studies should evaluate whether women with low measles titers are at increased risk of contracting the disease after exposure.