Differences in Factors Associated With Preterm and Term Stillbirth: A Secondary Cohort Analysis of the DESiGN Trial

OBJECTIVE: To identify whether maternal and pregnancy characteristics associated with stillbirth differ between preterm and term stillbirth. DESIGN: Secondary cohort analysis of the DESiGN RCT. SETTING: Thirteen UK maternity units. POPULATION: Singleton pregnant women and their babies. METHODS: Multiple logistic regression was used to assess whether the 12 factors explored were associated with stillbirth. Interaction tests assessed for a difference in these associations between the preterm and term periods. MAIN OUTCOME MEASURE: Stillbirth stratified by preterm (<37+0 weeks') and term (37+0-42+6 weeks') births. RESULTS: A total of 195 344 pregnancies were included. Six hundred and sixty-seven were stillborn (3.4 per 1000 births), of which 431 (65%) were preterm. Significant interactions were observed for maternal age, ethnicity, IMD, BMI, parity, smoking, PAPP-A, gestational hypertension, pre-eclampsia and gestational diabetes but not for chronic hypertension and pre-existing diabetes. Stronger associations with term stillbirth were observed in women with obesity compared to BMI 18.5-24.9 kg/m2 (BMI 30.0-34.9 kg/m2 term adjusted OR 2.1 [95% CI 1.4-3.0] vs. preterm aOR 1.1 [0.8-1.7]; BMI ≥ 35.0 kg/m2 term aOR 2.2 [1.4-3.4] vs. preterm aOR 1.5 [1.2-1.8]; p-interaction < 0.01), nulliparity compared to parity 1 (term aOR 1.7 [1.1-2.7] vs. preterm aOR 1.2 [0.9-1.6]; p-interaction < 0.01) and Asian ethnicity compared with White (p-interaction < 0.01). A weaker or lack of association with term, compared to preterm, stillbirth was observed for older maternal age, smoking and pre-eclampsia. CONCLUSION: Differences in association exist between mothers experiencing preterm and term stillbirth. These differences could contribute to design of timely surveillance and interventions to further mitigate the risk of stillbirth.