Maternal smoking at first prenatal visit as a marker of risk for adverse pregnancy outcomes in the Qikiqtaaluk (Baffin) Region.

INTRODUCTION: In Nunavut, 60-80% of pregnant women report smoking in pregnancy, a rate five times the Canadian average. Nunavut also has the highest rates of preterm birth and low birth weight infants in Canada. The present study assessed whether the number of cigarettes smoked per day, as recorded in the first trimester, influenced birth outcomes.
METHODS: Maternal-newborn charts were reviewed for infants born between 1 January 2003 and 31 December 2005 to at least one Inuit parent in the Qikiqtaaluk (Baffin) region of Nunavut. Smoking data, as reported by the mother at an early prenatal visit, were extracted from the prenatal record. Birth outcomes including birth weights (for term births), low birth weight, small for gestational age births and rates of preterm birth, were analysed according to category of reported number of cigarettes smoked (0, 1-5, 6-10, and >10 per day). Maternal age, alcohol and street drug use were also assessed for each category of smokers. Statistical analysis among groups was carried out.
RESULTS: Of 918 births meeting the study criteria, more than 80% of women reported smoking. For 80% of those, the amount smoked per day was available. Non-smokers and women smoking less than 5 cigarettes daily had perinatal outcomes equal to or better than Canadian averages for low birth weight, small for gestational age, and preterm birth. Furthermore, average birth weights at term significantly decreased from 3681 g for non smokers to 3310 g for those smoking more than 10 cigarettes per day. Compared with non-smokers, women in the highest smoking category (>10 cigarettes daily) had a six-fold increase in low birth weight infants (OR 6.7, 95% CI 2.3-19.6), almost a four-fold increase for small for gestational age births (OR 3.7, 95% CI 1.6-8.8) and twice the chance of a premature birth compared with non-smokers (OR 2.14, 95% CI 1.1-4.2). Those in the highest smoking category were also most likely to report alcohol and other substance use.
CONCLUSIONS: Inuit women who reported not smoking, or smoking less than 5 cigarettes per day had birth outcomes equal or superior to average Canadian outcomes in each category evaluated. Those women reporting smoking more than 10 cigarettes daily had significantly increased risk for preterm birth, low birth weight and small for gestational age infants. Because those in the highest smoking category also reported the highest rates of alcohol and other substance use, it is likely that a combination of factors assessed in this study influenced the outcomes. Along with public health preventative measures to reduce smoking directed to this high risk group, other contributing factors for adverse birth outcomes need to be assessed more fully to understand the complex interactions that lead to increased smoking, substance use and, therefore, adverse birth outcomes. Furthermore, evidence from this study suggests that smoking more than 10 cigarettes per day, reported at first prenatal visit, may provide a marker for those women at highest risk of poor outcomes, which could provide direction for focused public health efforts.