The prevalence of preterm deliveries in Berlin has not changed over 7 years: the impact of multiple births.

The problem of preterm deliveries has worsened in developed countries over the past decade. To evaluate whether multiple deliveries had an impact on this development, we analyzed the data of the Berlin Perinatal Survey from 1993-1999 for 206,308 deliveries. The prevalence of preterm deliveries was fairly constant during this period, and the proportion of preterm deliveries in the case of multiples remained constant. But the prevalence of preterm neonates increased significantly in Berlin due to an increased prevalence of multiple births. There was a significant increase of mothers aged over 30, of German nationality, and with preceding infertility treatment, while the prevalence rates of nearly all other risk factors for prematurity decreased over time. The risk of infertility treatments resulting in multiple deliveries increased in these years. On average, infertility treatment led to an about 10 times higher risk of producing multiples than singletons OR (95% CI) of 9.6 (8.6-10.6).