This investigation is designed to differentiate between the contributions of prenatal psychological stress and physical strain or exertion on low birth weight and preterm births. Our preliminary studies have demonstrated that higher levels of urinary catecholamines are detected in patients with higher mental stress scores and that physical activity appears to reverse these changes. Over the next three years 670 women will be assessed at 3 intervals in pregnancy and 4-6 weeks postpartum, and data collected about prenatal risk, anxiety, biochemical and biophysical indicators of stress, labor, delivery and neonatal outcome.