Causal mediation analysis
The causal mediation analysis was performed to disentangle the total effect of chronic hypertension-perinatal mortality association, with preterm delivery as the potential mediator (Table 3 ). Much of the TE of perinatal mortality and its component mortalities was mediated through preterm delivery. The indirect effect was greatest for perinatal mortality and stillbirth. Given the strong mediation component of the chronic hypertension-mortality association that operates through preterm delivery, the PE estimate is correspondingly high: 87% (95% CI 84, 90).