摘要：Objectives. We assess whether population-wide folic acid fortification policies were followed by a reduction of preterm and early-term birth rates in Québec among women with short and optimal interpregnancy intervals. Methods. We extracted birth certificate data for 1.3 million births between 1981 and 2010 to compute age-adjusted preterm and early-term birth rates stratified by short and optimal interpregnancy intervals. We used Joinpoint regression to detect changes in the preterm and early term birth rates and assess whether these changes coincide with the implementation of population-wide folic acid fortification. Results. A change in the preterm birth rate occurred in 2000 among women with short (95% confidence interval [CI] = 1994, 2005) and optimal (95% CI = 1995, 2008) interpregnancy intervals. Changes in early term birth rates did not coincide with the implementation of folic acid fortification. Conclusions. Our results do not indicate a link between folic acid fortification and early term birth but suggest an improvement in preterm birth rates after implementation of a nationwide folic acid fortification program. Preterm and early term birth are linked with a higher risk of infant mortality and morbidity, 1,2 and evidence suggests that rates of early delivery are increasing in many countries. 3 Short interpregnancy intervals, or the elapsed duration between a woman’s previous pregnancy and her next conception, are a well-known risk factor for preterm birth, and potentially early term birth. 4 Folate depletion from the previous pregnancy is hypothesized to underlie the relation between short interpregnancy intervals and preterm birth. 5 Research suggests that up to 20% of women are folate deficient at 6 months postpartum, the cutoff for short interpregnancy intervals. 6 In Canada, all grain products sold in the country were fortified with folic acid beginning in December 1998 because of overwhelming evidence that periconceptional folic acid prevents neural tube defects. 7 However, evidence conflicts on the role of periconceptional folic acid intake on preterm birth. 8 Moreover, recent research has suggested possible tumor-promoting effects of folic acid, 9 fueling controversy on whether mandatory fortification is a useful public health policy. 10,11 To contribute to this debate, we assessed whether Canada’s folic acid fortification program was related to lower rates of preterm and early term birth among women with short and optimal interpregnancy intervals after 1998. If folate depletion indeed causes early delivery, preterm and early term birth rates should decrease following folic acid fortification, and the magnitude of this decrease should be greater in women with short interpregnancy intervals.
