Smoking among older childbearing women - a marker of risky health behaviour a registry-based study in Finland

Background: Smoking during pregnancy is known to negatively affect pregnancy outcomes and it has been associated with numerous complications during pregnancy. Smoking is more common in younger pregnant women, but previous research has shown that adverse pregnancy outcomes related to older maternal age and smoking are even more harmful than with younger smokers. The aim of this study was to compare pregnancy outcomes among smoking and non-smoking pregnant women aged < 35 years and >= 35 years. Methods: In this registry-based study, the data were collected from three national Finnish health registries: Finnish Medical Birth Register, Finnish Hospital Discharge Register, and Register of Congenital Malformations between the years 1997 and 2008. The data included information on 80 260 women who were smoking during pregnancy, of which 11 277 (9%) were >= 35 years and 68 983 (13%) were < 35 years old. In multivariate modelling, the main outcome measures were preterm delivery, low Apgar scores at 1 min., low birth weight, small for gestational age, fetal death and preeclampsia. Results: Fewer older women smoked during pregnancy (9%) than younger women did (13%). Smoking increased the risk of adverse pregnancy outcomes, most in the older group. Multivariate logistic regression using non-smoking women aged < 35 years as a reference group indicated that smoking women < 35 years had higher rates of preterm delivery (OR 1.27 CI 1.20-1.35), SGA (OR 2.18 CI 2.10-2.26) and LBW (OR 1.73 CI 1.62-1.84). Non-smoking women = 35 had higher rates of preterm delivery (OR 1.15 CI 1.10-1.20), fetal death (OR 1.36 CI 1.12-1.64), preeclampsia (OR 1.14 CI 1.09-1.20) and LBW (OR 1.13 CI 1.07-1.19). Smoking women >= 35 had higher rates of preterm delivery (OR 1.60 CI 1.40-1.82), SGA (OR 2.55 CI 2.34-2.79), fetal death (OR 2.70 CI 1.80-4.05) and LBW (OR 2.50 CI 2.20-2.80). Conclusions: Smoking during pregnancy increased the risk of adverse pregnancy outcomes in all women, but the rates were the highest for women aged >= 35 years. Pregnant women aged >= 35 years smoking during pregnancy was a distinctly high risk group. Maternity care should identify these women and support them in cessation of smoking during the first trimester of pregnancy.