Parvovirus B19 Infection in Pregnancy
PhD thesis, University of Copenhagen, 1999
By Anne Kristine Valeur Jensen
Department of Epidemiology Research
Statens Serum Institut
Aims
The aim of this thesis was, in population-based designs, 1) to study factors that might have an influence on a pregnant woman’s risk of acquiring parvovirus B19 infection, 2) to establish incidence rates of parvovirus B19 infection in pregnant women during epidemic and non-epidemic periods, 3) to calculate the risk of spontaneous abortion after a first trimester parvovirus B19 infection, and 4) to investigate whether maternal parvovirus B19 infection during pregnancy affected birth characteristics, infant morbidity and infant mortality.
Methods
Within a population-based group of 40,050 pregnant women, we undertook a) a cross-sectional study of seroprevalence of parvovirus B19 and risk factors for past infection, b) a longitudinal study of seroconversions and disease determinants, and c) a nested case-control study of first trimester infections in cases of spontaneous abortions and control pregnancies. Information from national registers provided information about outcome of pregnancies and morbidity and mortality in infants followed on average until 2.7 years after birth.
Findings
Sixty-five percent of pregnant women had evidence of past infection. Annual seroconversion rates among susceptible women during endemic and epidemic periods were 1.5% and 13.0%, respectively. Factors reflecting a woman’s level of contact with children were the most important risk factors for parvovirus infection. Risk of acute infection correlated with number of children in the household as follows: 0 children, relative risk (RR)=1 (reference), one child RR=3.2, two children RR=5.5, three or more children RR=7.5. Children aged 5-7 years resulted in the highest rate of seroconversion among mothers. Compared with other pregnant women, nursery school teachers had a 3.1-fold increased risk of acute infection. Overall, exposure from the pregnant woman’s own children was responsible for more infections than her occupational exposure (population-attributable
risk 55.4% and 6.0% respectively). The risk of foetal loss was doubled in women who experienced a first trimester infection, but of all foetal losses occurring after the first trimester only 0.13% were attributable to a first trimester parvirus B19 infection. During epidemic periods this figure might
increase to 1.15%. Among susceptible pregnant women those figures were 0.37%
and 3.33%, respectively, For special groups such as nursery school teachers more than 9% of their foetal losses might during epidemics be explained by B19 infection. Overall, birth characteristics (birth weight, gestational age at birth and Apgar scores) infant morbidity and mortality were unaffected by maternal infection.
Conclusions
The risk of parvovirus B19 during pregnancy is determined primarily by contact to own children. Infection during the first trimester may double a woman’s risk of foetal loss, but the impact on the overall rate of foetal losses occurring after the first trimester is very limited even during epidemics
of parvovirus B19 infection. Therefore, we suggest, during epidemics, to target prevention strategies towards susceptible women in early pregnancy belonging to high-risk groups, where a reduction in the contact to children is feasible.
Sidst redigeret 29. juni 2010