Cause	Reported association/mechanism	Mediator	Direct cause label	Mediator label	Effect
Unintended pregnancy	Unintended pregnancy has been associated with short IPI, independent of age, educational attainment and income7, 31	NA	Unintend_preg	NA	Short_IPI
Low income	Low income has been associated with short IPI independent of educational attainment or age31	NA	Low_income	NA	Short_IPI
Low educational attainment	Low educational attainment has been associated with short IPI31	NA	Low_education	NA	Short_IPI
Low occupation class/unemployment	Low occupation class/unemployment has been associated with short IPI32	NA	Low_occupation	NA	Short_IPI
Extreme maternal age	Younger15, 16, 17, 18, 19 or older (>30) maternal age has been associated with short IPI7, 32	NA	Mat_age	NA	Short_IPI
Maternal morbidity	Underlying maternal factors may contribute to previous loss, which may result in short IPI33	Previous fetal/neonatal loss	Mat_morbid	Prev_loss	Short_IPI
Parity	Short IPI has been associated with high parity7, 32	NA	High_Parity	NA	Short_IPI
Smoking	Maternal smoking has been associated with short IPI32	NA	Smoking	NA	Short_IPI