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Show Risk Factors Associated with Low Birth Weight Risk factors for low birth weight have been identified; however, many are only correlates and not proximal causes. Low birth weight is largely associated with preterm birth with approximately 67% of all low birth weight infants in Utah classified as preterm. Demographic Factors Younger and older mothers tend to have the highest percentage of low birth weight infants. For births occurring during 1989-1997 in Utah, birth certificate data indicate that mothers under the age of 15 had the highest percentage of low birth weight births at 11.3%, followed by 16-17 year olds at 9.2% and 18-19 year olds at 8.3%. Mothers who are 40+ years old have a low birth weight percentage of 7.5%. Those between the ages of 25 and 39 years had the lowest percentage of low birth weight at approximately 5.4% (Bureau of Vital Records, 1999a). Low birth weight percentages vary among racial and ethnic groups. For births during 1989-1997 in Utah, Black women had a notably higher percentage of low birth weight births at 11.6% compared to 7.6% for white Hispanic, 6.8% for Asian/Pacific Islander, 5.9% for American Indian, and 5.9% for white non-Hispanic women (Bureau of Vital Records, 1999a). The high percentage of low birth weight births among Black women in Utah follows the national trend. Utah data indicate that the percentage of low birth weight was highest for mothers with the lowest median household income. Women with median household incomes of less than $20,000 had a low birth weight percentage of 7.2% compared with 5.5% for women with incomes of $60,000 or more (Bureau of Vital Records, 1999b). For the years 1989-1997 in Utah, unmarried women had a low birth weight percentage of 9.3% compared to married women with a percentage of 5.5% (Bureau of Vital Records, 1999a). Maternal educational attainment is associated with lower low birth weight percentages. Women in Utah without a high school diploma had a low birth weight percentage of 9.3% compared to 6.4% for women with a high school diploma (Bureau of Vital Records, (1999a). Medical Risks Medical risks prior to or during pregnancy may be related to low birth weight. Low pre-pregnancy weight has been associated with low birth weight (Institute of Medicine, 1992). Women with low pre-pregnancy body mass index (BMI) have a higher incidence of low birth weight births compared to women with normal or higher pre-pregnancy BMI. Utah women who were underweight for height prior to pregnancy had 8.1% low birth weight births compared to women who were not underweight prior to pregnancy with 5.5% low birth weight births (Bureau of Vital Records, 1999a). Nationally the numbers of infants born from higher order gestation pregnancies (triplets, quadruplets, etc.) have increased dramatically. This trend is due in part to older women giving birth and to increased use of artificial reproductive technologies (ART) such as in vitro fertilization and ovulation induction (National Center for Health Statistics, 1998). The incidence of low birth weight in multiple gestation pregnancies is directly associated with the number of fetuses in a pregnancy. In Utah, it is difficult to note trends in multiple gestation pregnancies because of small numbers. In 1997, there were 1,000 multiple births including 44 sets of triplets. From 1989 to 1997, twin births in Utah increased by 23.5%, slightly higher than the 20.9% increase in all births in the state During the years 1989 through 1997, 53.4% of all multiple births were low birth weight, with 52% of twins and 95% of triplet and quadruplet births being low birth weight compared to 4.9% among singleton births. Concurrently, the rate of low birth weight multiples increased from 504.9 per 1,000 live births in 1989 to 592.2 per 1,000 live births in 1997 (Bureau of Vital Records, 1999a). Low birth weight births are largely directly related to preterm birth (birth before 37 weeks' gestation). Of all low birth weight infants born in 1997 in Utah, approximately 67% were born prematurely, while 99% of the extremely low birth weight infants (less than 1,000 grams) were born preterm (Bureau of Vital Records, 1999a). Preterm delivery is known to be associated with 42 |