Stress and preterm birth: biological and vascular mechanisms affecting the feto‐placental circulation and the length of gestation

Preterm birth is the leading cause of perinatal morbidity and mortality. Women experiencing high levels of stress in pregnancy are at an increased risk of preterm delivery. This review examines the biological pathways of the maternal stress response, in particular, the functioning of the maternal hypothalamic–pituitary–adrenal axis, and investigates the role of the placenta in altering this response mechanism. Furthermore, the impact of the products of hypothalamic–pituitary–adrenal axis on the blood flow resistance of the feto‐placental arteries is explained. Prior Doppler studies of maternal stress were reviewed. The study of correlations between maternal stress and resistive indices of feto‐placental arteries was common themes in these studies. Their conclusions, however, were inconsistently explained by their methodological differences and limited control for potential confounders. The biological mechanisms of stress control provide the impression that it is plausible that antenatal stress could affect the placental function and influence preterm delivery, but to date, this has not been conclusively established. If the investigation is further expanded to include measures of fetal biometry, additional blood vessels and an assessment over a longer period in gestation, subtle changes in the feto‐placental blood supply may be revealed, and a link to preterm birth is feasible.