摘要：Objectives. We sought evidence to support the hypothesis that advancing maternal age is potentially causing a rise in preterm birth (PTB) rates in high-income countries. Methods. We assessed maternal age-specific trends in PTB using all singleton live births in Denmark (n = 1 674 308) and Quebec (n = 2 291 253) from 1981 to 2008. We decomposed the country-specific contributions of age-specific PTB rates and maternal age distribution to overall PTB rates over time. Results. PTB rates increased from 4.4% to 5.0% in Denmark and from 5.1% to 6.0% in Quebec. Rates increased the most in women aged 20 to 29 years, whereas rates decreased or remained stable in women aged 35 years and older. The overall increase over time was driven by age-specific PTB rates, although the contribution of younger women was countered by fewer births at this age in both Denmark and Quebec. Conclusions. PTB rates increased among women aged 20 to 29 years, but their contribution to the overall PTB rates was offset by older maternal age over time. Women aged 20 to 29 years should be targeted to reduce PTB rates, as potential for prevention may be greater in this age group. Preterm birth (PTB) rates are rising in many high-income countries, 1–5 but international comparisons that seek to understand the underlying reasons for the increase are lacking. It has been proposed that the rise in PTB is partly attributable to an increase in maternal age, 6 as women in Western countries increasingly delay pregnancy to later in life. 7–9 Several studies have shown strong associations between advanced maternal age and PTB, 10–12 but other studies only adjust for this variable, 13,14 making it difficult to determine the extent to which changes in maternal age are in fact responsible for the increase in PTB rates over time. The United States is the only country that has assessed the contribution of maternal age to changes in PTB rates, but older maternal age accounted for only a small portion of the increase, 1,15 a finding at odds with the notion that older age is driving the increase. Birth rates at advanced maternal ages, however, tend to be much lower in the United States than in other high-income countries. 16 A better understanding of how maternal age-specific PTB rates contribute to trends in overall PTB rates in other countries could help provide international goals for the reduction of PTB. PTB is major cause of infant morbidity and mortality, 2,17 with significant impact on health and development throughout life 18,19 and considerable economic costs to society. 1 Thus, the importance of assessing demographic contributions of population distribution to worldwide trends in PTB is easily justifiable. As a first step in achieving this goal, we sought to determine the contribution of older maternal to PTB rates over time in Denmark and Canada, 2 high-income areas characterized by advancing maternal age and rising PTB rates. 8,20 These countries are similar in respect to universal access to care but differ regarding maternal age distribution and age-specific PTB rates.
