Does an abortion increase the risk of intrapartum infection in the following pregnancy?

Spontaneous and induced abortions have been suggested to increase the risk of intrapartum infection in the following pregnancy. We conducted a case-control study using data from the Washington State Birth Registry for the years 1989-1991. The study population comprised women delivering a singleton livebirth. A case was defined by the presence of intrapartum fever (N = 2,550). Controls (1:3) were selected from the remaining births (N = 7,326). We calculated Mantel-Haenszel summary odds ratios by stratified analysis. We evaluated the validity of intrapartum fever recorded on the birth certificate using data from an ongoing case-control study on clinical amnionitis in Washington State. We found intrapartum fever to be highly specific (0.98) and moderately sensitive (0.57) for a diagnosis of clinical amnionitis. We saw no increased risk of intrapartum fever after a fetal loss or termination when using women with no prior pregnancy as the reference group. On the other hand, we found a threefold elevated risk for both induced and spontaneous abortion when using women with a prior livebirth as the reference group. Our findings indicate that an abortion in a woman's first pregnancy does not have the same protective effect of lowering the risk for intrapartum infection in the following pregnancy as does a livebirth.