Perinatal mortality among term births: Informing decisions about singleton early term births in Western Australia.

Background: To minimise the risk of perinatal mortality, clinicians and expectant mothers must understand the risks and benefits associated with continuing the pregnancy.

Objectives: Report the gestation-specific risk of perinatal mortality at term.

Methods: Population-based cohort study using linked health data to identify all singleton births at gestations 37-41 weeks, in Western Australia (WA) from 2009 to 2019. Lifetable analysis was used to combine the risk of each type of perinatal mortality and calculate the cumulative risk of perinatal mortality, termed the perinatal risk index (PRI). Rates of antepartum and intrapartum stillbirth and neonatal death, as well as the PRI, were examined for each gestational week at term by non-Aboriginal and Aboriginal ethnicity. For non-Aboriginal women, rates were also examined by time-period (pre- vs. post-WA Preterm Birth Prevention Initiative (the Initiative) rollout), primiparity, and obstetric risk.

Results: There were 332,084 singleton term births, including 60 perinatal deaths to Aboriginal mothers (3.2 deaths per 1000 births to Aboriginal mothers) and 399 perinatal deaths to non-Aboriginal mothers (1.3 deaths per 1000 births to non-Aboriginal mothers). For non-Aboriginal women, the PRI was at its lowest (PRI 0.80, 95% CI 0.61, 1.00) at 39 weeks gestation. For Aboriginal women, it was at its lowest at 38 weeks (PRI 2.43, 95% CI 0.48, 4.39) with similar risk at 39 weeks (PRI 2.68, 95% CI 1.22, 4.14). The PRI increased steadily after 39 weeks gestation. The risk of perinatal mortality was higher among Aboriginal women. The gestation-specific perinatal mortality rates were similar by the time-period, primiparity and obstetric risk.

Conclusions: The gestational ages at term associated with the lowest risk of perinatal mortality reinforce that the recommendation not to deliver before 39 weeks without medical indication is applicable to both Aboriginal and non-Aboriginal women giving birth in WA. There was no increase in the perinatal mortality rate associated with the introduction of the Initiative.