Factors associated with maternal smoking during early pregnancy: relationship to low-birth-weight infants and maternal attitude toward their pregnancy Kohta SUZUKI, M.D., Ph.D.; Taichiro TANAKA, M.D., Ph. D.; Naoki KONDO, M.D., Ph. D.; Junko MINAI,M.L.S.; Miri SATO, M.L.S.; Zentaro YAMAGATA, M.D., Ph.D. Department of Health Sciences, School of Medicine, University of Yamanashi, 1110 Shimokato, Chuo, Yamanashi , Japan Introduction Recently, Japan has witnessed an increase in the number of low birth weight (LBW) infants. In 1975, the incidence of male and female infants weighing under 2500 g at birth was 4.7% and 5.5% of the total births, respectively, whereas in 2003, this percentage increased to 8.1% and 10.1%, respectively. (Figure 1) The relationships between maternal smoking during pregnancy and each of the prenatal outcomes, namely, LBW, small for gestational age (SGA), and preterm birth, have been reported in many previous studies. To prevent LBW from the viewpoint of clinical and public health, it is important to further investigate maternal smoking during pregnancy as a risk factor for LBW. We previously identified maternal negative attitudes toward pregnancy and maternal smoking as independent risk factors for LBW infants in a community-based case-control study. Data from a national survey on maternal smoking during pregnancy in the US indicated that the rate of maternal smoking during pregnancy was 19.5% in 1989; this rate decreased to 11% in A similar survey in Canada also revealed a recent decrease in this rate. A decrease in the international rate of maternal smoking during pregnancy has been reported. However, in Japan, the number of women who smoked during pregnancy increased. The rate of maternal smoking during pregnancy was 5.6% in 1990, and this rate increased to 10.0% in Moreover, the number of young Japanese women who are likely to smoke has increased recently. Therefore, it is very important to prevent smoking, particularly in pregnant or young women in Japan. In this study, we used data from a longitudinal study to confirm the risk factors of LBW, such as maternal negative attitudes during pregnancy, which were previously identified by our case-control study. Moreover, this study aims to clarify the relationship between maternal smoking and other maternal lifestyle or pregnancy factors. (%) Figure 1: Rate of infants with low birth weight (LBW) in Japan (From Vital Statistics of Japan 2004; Statistics and Information Department, Minister's Secretariat, Ministry of Health, Labour and Welfare) Methods Participants and study design: The study population comprised pregnant women who registered their pregnancy at the city office between January 01, 1995 and July 31, 2000, and their children in Koshu City, Yamanashi Prefecture, Japan. These individuals were participants of Project Koshu—a dynamic prospective cohort study of pregnant women and their children in a Japanese rural area. (Figure 2) Exposure: Parental lifestyle immediately before pregnancy and during early pregnancy, including smoking status during early pregnancy, was assessed based on a self-report questionnaire administered at the time of pregnancy registration. In this study, we considered the following parameters as independent variables: sex of the child, birth order of the children, gestational age (weeks) at delivery, maternal age, maternal height, maternal body mass index (BMI) in the nonpregnant state, occupational status, smoking habits during early pregnancy, alcohol consumption during early pregnancy, breakfast habits, gestational age (weeks) at the time of pregnancy registration, and smoking habits of the partner during early pregnancy. Maternal body height and weight in the nonpregnant state were obtained from the Maternal and Child Health Handbook; these data were recorded in this handbook by the attending obstetrician or midwife. Main outcome measures and statistical analysis: Odds ratio (OR) was calculated with a 95% confidence interval (CI) for LBW and maternal smoking during early pregnancy by using a logistic multivariable regression analysis based on maternal factors. All analyses were conducted using SAS software, version 8.02 (SAS Institute Inc., Cary, North Carolina, USA). Figure 2: Project Koshu: A dynamic prospective cohort from registration of pregnancy

Results Participants: In this study, 1,242 pregnant women responded to the questionnaires administered at pregnancy registration. Of these, infant data were collected from 1,015 mothers (follow-up rate, 81.7%). Smoking during early pregnancy was reported by 63 (6.2%) mothers. The number of LBW infants was 70 (6.9%). Analysis 1: Association between maternal lifestyle habits and LBW infants (Table 1) Analysis 2: Association between maternal or partner’s lifestyle habits and maternal smoking during early pregnancy (Table 2) Conclusion In this cohort, maternal smoking during early pregnancy was significantly associated with LBW. Negative maternal attitude toward pregnancies was not an independent risk factor for LBW but was significantly associated with maternal smoking during early pregnancy. Skipping breakfast immediately before pregnancy, partner’s smoking habits during early pregnancy, and late registration of pregnancy were also significantly associated with maternal smoking during early pregnancy. To prevent maternal smoking during early pregnancy, it is necessary to monitor pregnant women who have a negative attitude toward pregnancy, who skipped breakfast immediately before pregnancy, or who registered their pregnancy after 12 gestational weeks. Acknowledgments The Project Koshu was conducted with the cooperation of the Koshu City administration office. We thank the public health nurses working at Koshu City for their collaboration in this study. Figure 3: Results and interpretation of this study: association between LBW and maternal factors.