Smoking during pregnancy from 1999 to 2004: a study from the Medical Birth Registry of Norway

Background. The aims of the study were to describe changes in smoking habits and evaluate secular trends among all Norwegian pregnant women during the period 1999-2004. We wanted to investigate whether there was a general decline in smoking habits among pregnant women. We also wanted to identify population subgroups with diverging trends. Methods. The Medical Birth Registry of Norway (MBR) has national coverage of all births of 16 or more gestational weeks. Since 1999, women have been asked about tobacco smoking at the beginning and at the end of pregnancy. We included records from 304,905 women giving birth in the period January 1999 through April 2004. Women born outside Norway were handled separately. The selection left a dataset containing 259,573 Norwegian-born women. Results. We obtained information on smoking habits from 86% at the end of pregnancy. Among those, the daily smoking prevalence was reduced from 17.3% in 1999-2001 to 13.2% in 2002-2004. Higher smoking prevalence was found among multiparous (3+), teenage mothers, single women, and women with low educational level. Conclusions. From 1999 to 2004, a substantial decline in smoking prevalence among Norwegian pregnant women was identified in all subgroups. However, an increasing social polarisation with regard to education and smoking habits was observed in the study period. In order to reduce the smoking-related risks for unsuccessful pregnancy outcome, special attention should be paid to smoking habits among multiparous, teenage women, single women and women with low education.