Table 1 shows estimates of prevalence of low birth-weight, IUGR, and preterm delivery from three major multicountry studies: the WHO Antenatal Care Trial, the WHO Collaborative Study on Pregnancy Outcomes, and the WHO Misoprostol Trial. The data presented demonstrate that the distribution of low birthweight varies across populations, and the observed differences are due to the varying contribution of preterm delivery and IUGR to the total rates of low birthweight. Rates of low birthweight are higher in developing than in developed countries, as shown by the data presented in Table 2. Data from 11 developed areas and 25 developing ones indicate that rates of low birthweight steadily increase as the level of development decreases. The observed differences in low birthweight rates between geographical areas are enormous, with rates ranging from as low as 3.6% in Sweden to as high as 43% in Mumbai, India. Importantly, a global review of the magnitude of the problem demonstrates that many countries currently exceed the internationally recognized cutoff levels for triggering public health action (IUGR >20% and low birth-weight (LBW) >15%). Most of low birthweight infants born in developed countries are the result of preterm delivery, whereas in developing countries they are more likely to be IUGR infants. In addition, differences in the distribution of low birthweight are observed at country level, as indicated by the higher prevalence of low birthweight (due mainly to pre-term delivery) among African Americans compared to other ethnic groups in the United States.
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