Occurrence and determinants of trimethoprim/sulfamethoxazole use in pregnancy.

Objective: To estimate the rate of prescription trimethoprim/sulfamethoxazole use in pregnancy, and to analyse the association between maternal characteristics and use of trimethoprim/sulfamethoxazole in pregnancy.

Methods: A population-based study was conducted based on a 50% random sample of women who gave a birth in Saskatchewan between 1 January 1997 and 31 December 2000. The rate of trimethoprim/sulfamethoxazole use during pregnancy was estimated. The exposure in each trimester was also estimated. Associations between maternal characteristics and pregnancy trimethoprim/sulfamethoxazole use were evaluated using multiple logistical regression with adjusted odds ratios (ORs) and 95% confidence intervals (CIs) as the association measures.

Results: A total of 18,575 women who gave a birth in Saskatchewan during the study period were included in the analysis. Among them, 596 (3.2%) had at least 1 prescription for trimethoprim/sulfamethoxazole during pregnancy, 389 (2.1%) in the first trimester, 208 (1.1%) in the second trimester, and 195 (1.1%) in the third trimester. Women with chronic health conditions (6.2%) had a 2-fold increased risk of exposure compared to women without a chronic health condition (2.8%). Younger women (<20 years) with parity >/=3 and women on Saskatchewan assistance plan were also at increased risk. There were variations in exposure by trimester. For example, teenage women without chronic health conditions were at increased risk of use in the second and third trimester.

Conclusions: Some 3.2% of women are exposed to trimethoprim/sulfamethoxazole during pregnancy. Women with chronic health problems, of younger age, and of lower socioeconomic status are at elevated risk of exposure to trimethoprim/sulfamethoxazole during pregnancy.