The increasing incidence of moderate preterm births (32-36 gestation weeks) might reflect a more general tendency toward a shortening of the gestational length occurring also in the term births (37 + gestation weeks). We examined all Italian 1st live born singletons (n = 2,356,365) and found that from 1990 to 1998 the births of 40 + gestation weeks decreased from 60.7 to 51.7% and among term births the average gestation weeks decreased from 39.74 to 39.55. In term pregnancies the effect of low education and advanced age of the mother in decreasing the gestational length persisted over time, but, independently of the maternal factors, the pregnancies experienced a progressive shortening. The finding, if confirmed for other countries, should deserve further investigations on possible determinants, as improved estimates of gestational age through the widespread use of prenatal ultrasound or diffusion of hazardous and stressing working and living conditions.