Increased risk of active tuberculosis during pregnancy and postpartum: a register-based cohort study in Sweden

Abstract

Rationale: Studies investigating the risk of active tuberculosis (TB) in association with pregnancy have not been conclusive. We aimed to investigate this risk in a large retrospective register-based cohort study in Sweden.

Methods: Data from women of 15-49 years of age who had given birth in Sweden between 2005 and 2013 were extracted from the national childbirth register and linked to the national TB register. Cohort time was divided into three exposure periods: during pregnancy, six months (180 days) postpartum and time neither pregnant nor postpartum. We calculated incidence rates (IRs) per 100 000 person-years for each period and incidence rate ratios (IRRs) with IRs neither pregnant nor postpartum as the reference.

Results: The cohort included 649 342 women, of whom 553 were registered as cases of active TB, 389 when neither pregnant nor postpartum, 85 during pregnancy and 79 when postpartum. Overall IRs were 9, 12 and 17 cases per 100 000 person-years, respectively, giving IRR 1.4, 95% CI 1.1-1.7 (during pregnancy) and IRR 1.9, 95% CI 1.5-2.5 (when postpartum). Stratification by TB incidence in country of origin showed that the increased risk was concentrated amongst women from countries with a TB incidence of 100 or higher, where IRs per 100 000 person-years were 137 (when neither pregnant nor postpartum), 182 (during pregnancy) and 233 (when postpartum).

Conclusion: We show a significant increase in risk of active TB during both pregnancy and postpartum in women from high incidence countries and recommend TB screening in pregnant women belonging to this risk group.

FIGURE 1

Timeline for the study of tuberculosis (TB) risk in pregnant women aged 15–49 years in Sweden for the period 2005–2013, with two examples of how contribution of time was stratified. Time was divided into three different periods: ‘pregnancy’, ‘postpartum’ and ‘time not pregnant or postpartum’. In the analysis of women from high incidence countries, ‘time not pregnant or postpartum’ was divided further into two periods: ‘before 1st pregnancy’ and ‘other time not pregnant or postpartum’, and also stratified by age group. Woman A was 22 years old at the start of the study and contributed time to age group 20–29 until she turned 30 years old, whereupon she contributed to age group 30–39. Woman B entered the study when she turned 15 years old and contributed time to age group 15–19 until she turned 20, whereupon she contributed to age group 20–29.

FIGURE 2

Tuberculosis (TB) incidence rate ratios (IRRs) with 95% CIs in women from high TB incidence countries. Categories: ‘before 1st pregnancy’, ‘pregnancy’ and ‘postpartum’ (as compared to ‘other time not pregnant or postpartum’).

FIGURE 3

Tuberculosis (TB) incidence rate ratios (IRRs) with 95% CIs in women from high TB incidence countries, as stratified by age group (20–29 and 30–39 years). Categories: ‘before 1st pregnancy’, ‘pregnancy’ and ‘postpartum’ (as compared to ‘other time not pregnant or postpartum’).