摘要：Objectives . We studied the effects of twins and triplets on perinatal health indicators in the overall population in the 1980s and 1990s in Canada, England and Wales, France, and the United States. Methods . Data were derived mostly from live birth registration. We used rates, relative risks, and population attributable risks for twins and triplets separately. Results . In each country, the increase in multiple births, and the increase in preterm delivery among multiple births, contributed almost equally to the rise in or stabilization of the overall rates of preterm delivery. Twins contributed a much larger proportion of the preterm deliveries and low-birthweight newborns than did triplets. Conclusions . Twins have a major population-based impact on the trends of perinatal health indicators. (Am J Public Health. 2002;92:1323–1330) Despite programs and policies in a number of countries designed to lower the incidence of preterm birth (< 37 weeks of gestation) and low birthweight (< 2500 g), these adverse birth outcomes have not decreased in the past 10 to 15 years. In some countries, they have actually increased substantially. For example, in the United States between 1981 and 1997, the preterm birth rate increased by approximately 21%. 1 An increase has also been noted in Canada for preterm delivery 2 and in England and Wales for low birthweight. 3 This rise in the proportion of babies born too early or too small represents an important public health concern for a number of reasons. Preterm newborns account for about 70% of perinatal mortality, 4 and preterm survivors are still at increased risk for health and developmental problems. 5– 7 Furthermore, preterm and low-birthweight newborns are more likely to need intensive care, with the attendant emotional and financial costs. 8, 9 Over the past 10 to 15 years, the rates of multiple births have risen in many countries. 10, 11 Because multiple births are at high risk of resulting in preterm birth and low birthweight, 12, 13 their increasing incidence affects the overall rates of both conditions. Previous studies on the effects of multiple births have shown their important influence on pregnancy outcomes in some countries. 2, 14, 15 However, no study has explored the independent effect of twin and triplet deliveries on trends in preterm births and low birthweight from an international perspective; that is, in countries with different health indicators and health care systems. Furthermore, it is unclear how much of the overall impact is due to (1) the increase in the occurrence of multiple births and how much is due to (2) preterm delivery and low birthweight among multiple births. In this report, we examine trends in multiple live births and their impact on the rates of preterm delivery and low birthweight in the early 1980s and the late 1990s. This analysis was carried out in Canada, England and Wales, France, and the United States. Data were drawn from vital statistics or nationally representative surveys of births.
