Prevention of low birth weight is an important public health objective because of the long-term consequences to the child, family, and society. Active smoking has long been known to be one of the major causes of low birth weight. Because of problems with measuring an individual's exposure to environmental tobacco smoke (also known as secondhand smoke or passive tobacco smoke), it is less clear to which degree environmental tobacco smoke is a cause of low birth weight. Recently, laboratory methods have been developed that can measure substances in the blood which tell how much an individual has been in contact with environmental tobacco smoke over the past few days, even at very low levels of contact.
In our recent work with a small number of pregnant women in four counties in the San Joaquin Valley, we have used these new laboratory methods and found that nearly 85 out of 100 nonsmoking pregnant women had at least some contact with environmental tobacco smoke, and 6 out of 100 had high levels of contact. The average birth weight of infants of mothers who had high levels of contact with environmental tobacco smoke was one-quarter pound lighter than infants of those who had no measurable contact, or about half that seen with active cigarette smoking. We also found that with each lower level of contact, infant birth weight increased. There did not appear to be any safe level of contact. Because we had only a total of around 1,000 women in this earlier study, these conclusions are not very solid. In this grant application, we propose to enlarge the study by around 2,000 women to more definitively study whether environmental tobacco smoke is dangerous to the developing baby.
We propose conducting this study among approximately 3,000 pregnant women who enrolled in the State's prenatal screening program in April 1992, and who were residents of an eleven-county region predominantly in California’s San Joaquin, San Bernardino, and Riverside Valleys. Blood from these women has been stored in a freezer and will be analyzed in a laboratory to find out how much contact the women have had with environmental tobacco smoke during their pregnancies. This information will be linked to information from the live birth certificate on birth weight and other factors, and then analyzed. It will not be necessary to communicate with the women in order to do this study.
This study will tell us how much contact pregnant women are having with environmental tobacco smoke. We will see how much birth weight is reduced, if at all, by being in contact with different amounts of environmental tobacco smoke. We will find out if there are special groups of women who are more or less susceptible to any possible effects of environ-mental tobacco smoke. Using information from a special questionnaire given to some of the study women when they gave birth in the hospital in 1992, we will discover the places people come into contact with environmental tobacco smoke the most, like at home, work, or other places. It is our hope that the new information obtained from this study will be used by individuals, researchers, government workers, and politicians to appropriately guide future efforts at preventing and reducing tobacco's toll on human growth and development. |
The main objective of this study is to accurately measure the impact of environmental tobacco smoke (ETS) exposure during pregnancy on a variety of pregnancy outcomes. The study population derives from over 3,000 pregnant women who enrolled in California’s Maternal Serum Alpha-Fetoprotein prenatal screening program in April 1992 from a diverse eleven-county region of the state. Blood samples from these women were stored in a freezer and analyzed in a laboratory to find out how much contact the women had with ETS during their pregnancies. This information was linked to information from the live birth certificate on birth weight and other factors. Different analyses were conducted to determine how much birth weight is reduced, if at all, by being in contact with different amounts of ETS. We investigated whether there are special groups of women who are more or less exposed or susceptible to the effects of ETS. Using information from a special questionnaire given to some of the study women when they gave birth in the hospital in 1992, we identified the places pregnant women come in contact with ETS, like at home, work, or other places.
Through laboratory analysis of blood, we found that the highest levels of ETS exposure were in Black women, and the lowest levels were in Mexico-born Hispanic women. Generally, higher ETS exposures were associated with being younger, less educated, and poorer. According to self-report, the home was the main location where nonsmoking women were exposed to ETS.
The effects of ETS were varied. Across the range of ETS exposure, from least exposed to most exposed, we found that fetal death (after 19 weeks gestation) increased 3 times, preterm delivery (before 37 weeks gestation) doubled, low birth weight (less than 5.5 lbs) increased by 1.5 times, and mean birth weight declined by about one-fifth of one pound, or 3-4% of a baby’s overall weight at birth. There was no “safe” level below which ETS did not diminish birth weight. Blacks and women who consume high amounts of caffeine may be more susceptible to the effects of ETS than other subgroups of the population, but our study had too few numbers of such individuals to be sure.
These results suggest that policies be put into place or tightened to protect pregnant women and their unborn children from exposure to ETS. Further steps need to be taken to lower exposure to ETS in the home. Studies that don’t use objective measures of exposure to ETS may be unable to accurately quantify the true health effects of ETS. |