Us birth certificate

ABBREVIATIONS. LBW, low birth weight; API, Asian or Pacific Islander; CDC, Centers for Disease Control and Prevention; NSFG, National Survey of Family Growth.

Cigarette smoking during pregnancy has been associated with increased risk of miscarriage, intrauterine growth retardation, preterm birth, and reduced infant birth weight. Low birth weight (LBW; weight <2500 g) is a major predictor of infant mortality and childhood morbidity and mortality (1-6) and carries substantial costs. (7) Intensive educational efforts by the federal government, public health officials, and others have contributed to the increased awareness of the negative consequences of maternal smoking. (8,9) The mechanisms through which tobacco adversely affects pregnancy and birth weight have been described. (8-10) Beginning in 1989, data on birth certificates, available from the National Vital Statistics System, included questions on smoking during pregnancy. (11,12) This article describes and interprets trends and variations in tobacco use during pregnancy on the basis of information reported on birth certificates. We discuss our findings from birth certificate data in light of data from other sources to monitor smoking patterns among pregnant women. We also discuss how changes in the prenatal smoking questions on the birth certificate can be used to evaluate more effectively trends and variations in smoking during pregnancy. These findings can be useful in developing intervention strategies tailored for particular groups of women.

METHODS

We analyzed birth certificates for all infants who were born in 49 states and the District of Columbia, representing 87% of US births in 2000. (11,12) Data on smoking for California births were not included in this analysis because their birth certificate questions differed from the standard format. The basic source for detailed information on smoking during pregnancy is the 2-part question first added to birth certificates in 1989 and now included on the birth certificates of all states except California. (13) When the prenatal smoking question was first added to the birth certificate in 1989, 43 states and the District of Columbia reported this information; by 1994, the reporting area was composed of 46 states, New York City, and the District of Columbia. (12) The question asked whether the mother used tobacco during pregnancy and, if yes, the average number of cigarettes smoked per day. We examined first the correlates of maternal smoking, including maternal demographic and health characteristics, and then considered the consequences of smoking during pregnancy, focusing on the incidence of LBW for smoking and nonsmoking mothers. LBW infants include both infants who had intrauterine growth retardation and infants who were born preterm. The data presented here on LBW were based on singleton births only, to eliminate the effect of multiple births, which are at much higher risk of LBW regardless of other maternal characteristics. We also assessed trends and variations in prenatal smoking among population subgroups during the 1990s. In discussions of patterns by race and Hispanic origin, data for Hispanic women include all Hispanic women of any race; data presented by race are for non-Hispanic women.

RESULTS

Smoking during pregnancy declined steadily since 1989 according to birth certificate data. In 2000, 12.2% of women who gave birth reported tobacco use during pregnancy; compared with 19.5% in 1989, the rate in 2000 represents a 37% decline (Fig 1). Of the women who smoked in 2000, ~7 in 10 reported smoking less than half a pack of cigarettes daily, one fourth smoked between half a pack and a pack daily, and 3% smoked a pack or more. (11) During the 1990s, not only have prenatal smoking rates declined, but also the number of cigarettes women smoked during pregnancy has declined.

[FIGURE 1 OMITTED]

Correlates of Maternal Smoking

In 2000 as in earlier years, smoking rates differed considerably by maternal age with rates for women aged 25 and older significantly lower than rates for women in their teens and early 20s (Table 1 and Fig 1). Over the decade, rates generally dropped for women in all age groups with especially steep declines for women in the 25- to 39-year-old age group. During the mid-1990s, smoking rates during pregnancy rose for teenagers, but rates have since leveled off and declined modestly between 1999 and 2000. The rate for women in their early 20s changed little since the mid-1990s.

Prenatal smoking rates varied substantially among racial and Hispanic-origin populations (Table 1), ranging in 2000 from 2.6% of non-Hispanic Asian or Pacific Islander (API) women, 9.2% of non-Hispanic black women, 15.6% of non-Hispanic white women, and 20.5% of non-Hispanic American Indian women. Within non-Hispanic API and Hispanic subgroups, smoking rates varied greatly as well, for example, among non-Hispanic API women from 0.6% (Chinese) to 14.4% (Hawaiian) and among Hispanic women from 1.5% (Central and South American women) to 10.3% (Puerto Rican women; data not shown). (11) Not only did Hispanic and non-Hispanic API and black women have low rates of prenatal smoking, but also the consumption of cigarettes among smokers was considerably lower than among non-Hispanic white women. In 2000, just 14% to 15% of Hispanic, non-Hispanic API, and black women who smoked smoked half a pack of cigarettes or more, compared with 31% of non-Hispanic white women.

Disparities in smoking rates were particularly large among teenage population subgroups. For example, among teenagers 18 to 19 years old, the rate of smoking during pregnancy ranged from 4.6% for Hispanics to 30.8% for non-Hispanic whites. A factor contributing to the much lower overall smoking rates for Hispanic and non-Hispanic API women was the dramatically lower prenatal tobacco use among women who were born outside the 50 states and the District of Columbia (2.2%) compared with women who were born in the 50 states and the District of Columbia (14.3%).

Smoking rates during pregnancy differed strikingly according to maternal education. Women who attended but did not complete high school had the highest smoking rates, 25.5% overall in 2000, and 28.2% of women aged 20 and older in this education category. In contrast, only 2.0% of college-educated women were reported as smokers. Among women with 9 to 11 years of schooling, the disparities were particularly large by race and Hispanic ethnicity: 47.5% of non-Hispanic white women, 23.8% of non-Hispanic black women, and 5.6% of Hispanic women aged 20 and older smoked during pregnancy (data not shown).

Unmarried mothers had much higher prenatal smoking rates than married mothers, and the disparity widened substantially with advancing maternal age. Women who started prenatal care in the first trimester of pregnancy had the lowest smoking rates overall, but among older teenagers, smoking rates differed little by trimester in which prenatal care was begun. One fourth or more of women who received no prenatal care at all smoked during pregnancy.

Consequences of Maternal Smoking

The negative association of maternal smoking and infant birth weight has been shown in numerous studies based on birth certificate data as well as other sources. (1,3,14,15) In 2000, the incidence of LBW among singleton infants who were born to smokers was nearly double that for nonsmokers: 10.4% compared with 5.6%. The difference in LBW was observed for all age groups and for births to Hispanic and non-Hispanic white and black women. Women who smoked during pregnancy compose 21% of all LBW births compared with 12% of births of 2500+ g.

Generally, the LBW gap by smoking status widened with advancing maternal age, for all groups. Among LBW subgroups, prenatal smoking status seemed to have a greater impact on variations in moderately LBW (1500-2499 g) than very LBW (<1500 g; Table 2). Overall moderately LBW rates were 8.8% for births to smokers and 4.5% for births to nonsmokers; comparable very LBW rates were 1.6% and 1.1%, respectively.

The risk of LBW was also elevated for births to less educated women who smoked, even after controlling for maternal age. LBW rates for births to smokers were consistently higher than for births to nonsmokers, regardless of maternal age, race/Hispanic ethnicity, or education (tabular data not shown).

Among smokers, LBW rates rose steadily with increasing consumption of cigarettes. In 2000, 15.1% of births to women who smoked at least 1.5 packs of cigarettes were LBW, compared with 9.7% of births to women who smoked fewer than 5 cigarettes daily and 5.6% for births to nonsmokers.

DISCUSSION