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.