does stress cause preterm labor
The beginning of labor is a complex process that is not fully understood. Multiple hormones and body systems in both mother and baby are involved, and predicting when labor will start is very difficult. Because labor is complicated and hard to study, scientists can't say for sure that stress causes preterm labor. But there is an association. In other words, studies show that mothers who experience more stress are more likely to go into labor early, so stress increases a mother's risk of premature labor.
1 When stress happens matters: effects of earthquake timing on stress responsivity in pregnancy. American Journal of Obstetrics & Gynecology 2001;184:637-642.  Littleton H, Breitkopf C, Berenson A. Correlates of anxiety symptoms during pregnancy and association with perinatal outcomes: A meta-analysis.