Risk factors for late preterm and term stillbirth: A secondary analysis of an individual participant data meta-analysis

Objective: Identify independent and novel risk factors for late-preterm (28- 36 weeks) and term (=37 weeks) stillbirth and explore development of a risk-prediction model.Design: Secondary analysis of an Individual Participant Data (IPD) meta-analysis investigating modifiable stillbirth risk factors. Setting: An IPD database from five case- control studies in New Zealand, Australia, the UK and an international online study.Population: Women with late-stillbirth (cases, n = 851), and ongoing singleton pregnancies from 28 weeks' gestation (controls, n = 2257).Methods: Established and novel risk factors for late-preterm and term stillbirth underwent univariable and multivariable logistic regression modelling with multiple sensitivity analyses. Variables included maternal age, body mass index (BMI), parity, mental health, cigarette smoking, second- hand smoking, antenatal- care utilisation, and detailed fetal movement and sleep variables.Main outcome measures: Independent risk factors with adjusted odds ratios (aOR) for late-preterm and term stillbirth.Results: After model building, 575 late- stillbirth cases and 1541 controls from three contributing case- control studies were included. Risk factor estimates from separate multivariable models of late-preterm and term stillbirth were compared. As these were similar, the final model combined all late-stillbirths. The single multivariable model confirmed established demographic risk factors, but additionally showed that fetal movement changes had both increased (decreased frequency) and reduced (hic-coughs, increasing strength, frequency or vigorous fetal movements) aOR of still-birth. Poor antenatal- care utilisation increased risk while more- than-adequate care was protective. The area- under-the- curve was 0.84 (95% CI 0.82- 0.86).Conclusions: Similarities in risk factors for late-preterm and term stillbirth sug-gest the same approach for risk- assessment can be applied. Detailed fetal movement assessment and inclusion of antenatal- care utilisation could be valuable in late-stillbirth risk assessment.