Background: Interpregnancy interval (IPI) is a potentially modifiable risk factor for pregnancy outcomes, and short and long IPI may be associated with increased risk of pregnancy complications. Record linkage provides the only practicable means to investigate IPI effects, which requires large generalisable sample sizes and long follow-up time.
Aim: This study examined the effect of IPI on pre-eclampsia in Western Australia, with the aim to inform the evidence-base for IPI recommendations in high-income countries.
Methods: A longitudinal retrospective cohort study was conducted using linked records for all births from the WA Midwives Notification System and Hospital Morbidity Data Collection. Conditional logistic regression was used by matching 96,501 women with three consecutive singleton births at 20-44 weeks of gestation (two IPI per mother) between 1980 to 2015(inclusive).
Results: Among the included cohort 17,047(6%) had a diagnosis of pre-eclampsia. Additional 2818 pre-eclampsia cases were identified through linkage to hospital records. A between mother analysis estimated (AOR:0.90, 95% CI 0.82-0.97), (AOR:1.74, 95% CI 1.58-1.91) for IPI of 6-11 months and ≥ 60 months respectively (as compared to 18-23 months) for pre-eclampsia. Both unmatched and matched models estimated high odds of pre-eclampsia for long IPI. However, the matched model showed a much weaker effect of long IPI (≥60 months) on pre-eclampsia (AOR:1.38, 95% CI 1.14-1.67).
Conclusion: Our study does not support the existence of a causal effect of short IPI on pre-eclampsia. Data linkage improved ascertainment of the outcome measure. Results suggest 18-23 months may be optimal for avoiding complications in future pregnancies.