The psychological state of a pregnant woman has been related to her labor and delivery. Pregnancy is a time of inoreased anxiety in many women. The level of anxiety tends to increase in the last trimester of pregnanoy when the time for labor and delivery is drawing near.
McCullough '74, Susan B., "Preparation of Childbirth as a Behavior Modifier in Relation to the Viewing of a Film of Natural Childbirth" (1974). Honors Projects. Paper 18.