Smoking in early gestation or through pregnancy: A decision crucial to pregnancy outcome
Introduction
Smoking during pregnancy has constantly been reported to associate with adverse pregnancy outcomes, such as low birth weight (LBW) (Castles et al., 1999, Hammoud et al., 2005, Higgins, 2002, Lindley et al., 2000, Magee et al., 2004, Mohsin et al., 2003, Roquer et al., 1995, Wang et al., 1997), placental abruption (Ananth et al., 1996, Higgins, 2002, Mortensen et al., 2001) and placenta praevia (Ananth et al., 1996, Higgins, 2002, Mortensen et al., 2001). The effect of smoking on the risk of pre-eclampsia has also been studied widely, and it has been concluded that smoking reduces the risk of pre-eclampsia, but that the mediating mechanisms remain unclear (Castles et al., 1999, Conde-Agudelo et al., 1999, Hammoud et al., 2005, Higgins, 2002). The results of previous studies have suggested that giving up smoking during pregnancy prevents some smoking-related adverse pregnancy outcomes such as LBW and small-for-gestational-age (SGA) infants (Lindley et al., 2000, Mitchell et al., 2002).
The aim of this study was to assess pregnancy outcome when smoking was reduced to less than five cigarettes per day or continued during pregnancy, compared with pregnancy outcome of non-smoking women. We also studied maternal risk factors and socio-economic factors associated with smoking or reducing smoking during pregnancy. Possible confounding factors, such as maternal age, race, education, body mass index and previous pregnancy complications, have been investigated in several previous studies but, for example, alcohol consumption during pregnancy has usually not been considered (Ananth et al., 1996, Cnattingius et al., 1997, England et al., 2002, Higgins, 2002, Lindley et al., 2000, Mitchell et al., 2002, Wang et al., 1997). Our database contains comprehensive data on maternal behavior and pre-pregnancy health, and therefore in this study we had an opportunity to control for confounding of these factors in this study.
Section snippets
Methods
Data were collected regarding all women who gave birth at Kuopio University Hospital between 1989 and 2001, totaling 26,414 pregnancies. Women who reported smoking five cigarettes or more per day at 20 weeks of pregnancy were included in the group who continued to smoke during pregnancy. The “reduced smoking” group consisted of women who were smokers at baseline and had then reported that they have reduced smoking before 20 weeks of pregnancy to less than five cigarettes per day. These two
Results
Of the obstetric population, 73.5% did not smoke during pregnancy, 13.1% continued to smoke and 13.4% reduced smoking before 20 weeks of pregnancy. Of all women in this study, 87.8% were aged 18–35 years, being a low risk age for pregnancy, and the percentages in both study groups were similar to those in the entire study population. Prevalence of not smoking varied during the study period from the lowest 71.8% in 1992 to the highest 76.5% in 2000. Prevalence of reducing smoking varied from
Discussion
We studied the impact of reducing smoking before the 20th week of pregnancy and continuing smoking through pregnancy compared to non-smoking women's pregnancies. Additional risk of fetal growth restriction (SGA), low birth weight or low Apgar score associated with smoking was avoided by reducing smoking in the early weeks of gestation, but the increased risks of preterm birth or perinatal death were not. The prevalence of smoking during pregnancy was similar to that reported earlier in Finland (
Conclusion
We conclude that reducing smoking during pregnancy is most likely protective as regards some smoking-related adverse pregnancy outcomes such as growth restricted (SGA) infants, low birth weight and low Apgar score. The risk of adverse pregnancy outcomes of women who reduced smoking during pregnancy is closer to the risks of non-smoking than smoking women, even though their health behavior is closer to those who continue to smoke than non-smokers. Education and support in giving up smoking are
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