Birth Outcomes After Pertussis and Influenza Diagnosed in Pregnancy: A Retrospective, Population-Based Study.

Abstract

OBJECTIVE Adverse birth outcomes and the maternal severity of influenza in pregnancy are well documented but information on pertussis is limited. DESIGN Population-based linkage data were collected during 2001-2016. SETTING New South Wales, Australia. POPULATION OR SAMPLE A total of 1 453 037 singleton births. METHODS Cox regression was used to estimate the associations between pertussis or influenza during pregnancy and birth outcomes with adjustment of covariates. MAIN OUTCOME MEASURES Adverse birth outcomes (preterm birth and low birth weight). RESULTS Among 1 453 037 singleton births over 16 years, we identified pertussis in 925 (49; 5.3% hospitalised) and influenza in 2850 (1092; 38.3% hospitalised) women during pregnancy. Cases of pertussis were similarly distributed by trimester (32% 3rd) whereas 46% of influenza cases were in the 3rd trimester. Younger age, previous birth, and being overseas-born were associated with both pertussis and influenza, whereas identifying as Aboriginal or Torres Strait Islander, hypertension or diabetes before and during pregnancy, and a number of other factors were only associated with influenza. Both pertussis and influenza in pregnancy were associated with increased risk of preterm birth (pertussis: aHR = 1.30, 95% CI 1.01-1.68; influenza: aHR = 1.56, 95% CI 1.36-1.79) and these increased risks were greater when infections in the period within 2 weeks of birth were considered (pertussis: aHR = 2.36, 95% CI 1.26-4.41; influenza: aHR = 2.29, 95% CI 1.78-2.96). CONCLUSIONS Maternal pertussis and influenza infections close to the time of birth were associated with adverse birth outcomes. These findings highlight the benefits of vaccination during pregnancy.