Fetal growth and onset of delivery: A nationwide population-based study of preterm infants

Objective This study was undertaken to assess whether deviations from normal fetal growth are associated with spontaneous preterm delivery. Study design A population-based study was performed, using Swedish Medical Birth Register data from 1991 through 2001. The total population comprised 1,007,648 singleton births. Intrauterine-derived growth standards were used to identify individual standard deviation (SD) from expected birth weight. Spontaneous preterm infants were compared with infants born after spontaneous labor at term. Results were obtained by using multiple logistic regression analysis. Results Associations between smaller than population mean and spontaneous preterm birth were evident for all gestational age groups. The largest risk was found at 28 to 31 gestational weeks and birth weight less than −3 SD (OR: 13.3; 95% CI: 10.3-17.2). Spontaneous preterm infants born at 34 to 36 gestational weeks weighed 1 to 1.9 SD (OR: 1.1; 95% CI: 1.1-1.2) or 2 to 2.9 SD (OR: 1.6; 95% CI: 1.5-1.7) above the expected mean more often. Conclusion Deviation of fetal growth from the expected mean is associated with spontaneous preterm delivery.