Changes in characteristics of women who smoke during pregnancy: Missouri, 1978-88.

The Missouri birth certificate has had a question, "cigarettes smoked per day?" since 1978; the current data base contains more than 800,000 records. A comparison of the Missouri data for married mothers with the National Natality Survey (NNS) data shows mainly consistent findings between the two data sets. The Missouri data, however, also provided information on the smoking status during pregnancy of unmarried women that is not available from the NNS. The Missouri data show a substantial difference in the smoking rates of married (23.2 percent) and unmarried (40.9 percent) women. The highest smoking rates during pregnancy are found among unmarried women, ages 20-24, with less than a high-school education, and those with a fourth or higher order child. There has been a relatively small overall drop in the smoking rate from 1978-80 to 1986-88 (31.1 percent versus 27.5 percent). However, blacks and teenagers have had very substantial drops in smoking rates. There has been only a slight decrease for other high-risk groups such as white unmarried women, women with less than a high-school education, and those having a fourth or higher order birth. Missouri started using the new national standard birth certificate in 1989 with a differently worded smoking question. The percentage of women smoking and those smoking less than one pack per day in 1989 went down more than would be expected from the trend data. It appears that the new birth certificate question will provide a lower estimate of the percentage of mothers who smoke cigarettes than was acquired from the previous version on the Missouri certificate. The births in Missouri for which mothers' rate of smoking was unknown increased nearly fourfold to 0.9 percent.