Objectives: To evaluate the effect of physical workload and psychological demand on all preterm births, and to determine whether these risk factors have the same effect on different types of preterm birth (moderate versus very preterm birth) and different modes of delivery onset (spontaneous versus indicated preterm birth).
Methods: A case-control study was carried out in two public general hospitals in the Valencia Region, Spain. All preterm births (228) which occurred between 22 and 36 completed weeks of amenorrhea and 348 controls of 37 or more completed weeks of amenorrhea were included. The information was collected by interviewing women within 2 days of their giving birth. Physical workload, psychological demand, weekly working hours and daily time spent commuting between home and work were used as explanatory variables. A polytomous logistic regression was carried out.
Results: Exposure to medium or high level physical workload increases the risk of preterm birth, with an adjusted odds ratio (OR) of 1.59 and 2.31, respectively. The risk of moderate preterm birth was greater in women with a medium or high level of physical workload, OR: 1.73 and 2.35, respectively. The same trend was observed for very preterm birth. Physical workload showed a different effect on spontaneous and indicated preterm birth. The exposure to medium and high level physical workload increases the risk of indicated preterm birth, with an OR of 2.74 and 3.88, respectively. The same trend was seen in the case of spontaneous preterm birth. Psychological demands were not associated with preterm birth.
Conclusions: High physical exertion increases the risk of preterm birth in Spain. The magnitude of the effect of physical workload on moderate and very preterm birth is similar, but is higher on indicated preterm birth than on spontaneous preterm birth. Psychological demands show no effect on the risk of preterm birth.