How does stress contribute to spontaneous preterm birth?

• A. By increasing maternal physical activity
• B. By causing premature activation of the fetal HPA axis
• C. By improving placental blood flow
• D. By enhancing fetal development

Answer: (B)

Stress contributes to spontaneous preterm birth primarily through the mechanism of activating the fetal hypothalamic-pituitary-adrenal (HPA) axis prematurely. When a mother experiences significant psychological or physical stress, it can lead to the release of stress hormones such as corticotropin-releasing hormone (CRH) and cortisol. These hormones can stimulate the fetal HPA axis, triggering a series of physiological responses that may lead to preterm labor.

The activation of the fetal HPA axis can increase the production of prostaglandins and other factors that are associated with the onset of labor, thereby resulting in contractions and early delivery. This pathway highlights the complex interaction between maternal stress and fetal development, showcasing how maternal psychological states can influence pregnancy outcomes.

In contrast, the other options do not accurately represent the relationship between stress and preterm birth. Increased maternal physical activity typically does not lead to preterm birth and can be beneficial in maintaining a healthy pregnancy. Improving placental blood flow is generally associated with positive outcomes and, when functioning well, would not contribute to preterm delivery. Enhancing fetal development also contradicts the aim of understanding preterm birth, as stress typically negatively impacts fetal health and development.