The complex relationship between smoking in pregnancy and very preterm delivery

Abstract

, and the EPIPAGE Study GroupThe EPIPAGE Study Group (listed in the Appendix)Objective To assess the relationship between cigarette smoking during pregnancy and very preterm births, according to the main mechanisms of preterm birth. Design Case -control study (the French Epipage study).Setting Regionally defined population of births in France.Population Eight hundred and sixty-four very preterm live-born singletons (between 27 and 32 completed weeks of gestation) and 567 unmatched full-term controls. Methods Data from the French Epipage study were analysed using a polytomous logistic regression model to control for social and demographic characteristics, pre-pregnancy body mass index and obstetric history.The main mechanisms of preterm delivery were classified as gestational hypertension, antepartum haemorrhage, premature rupture of membranes, spontaneous preterm labour and other miscellaneous mechanisms. Main outcome measures Odds ratios for very preterm birth for low to moderate (1 -9 cigarettes/day) and heavy ( 10 cigarettes/day) maternal smoking in pregnancy, estimated according to the main mechanisms leading to preterm birth. Results Smokers were more likely to give birth to very preterm infants than non-smokers [adjusted odds ratio (aOR) 1.7, 95% confidence interval (CI) 1.3 -2.2]. Heavy smoking significantly reduced the risk of very preterm birth due to gestational hypertension (aOR 0.5, 95% CI 0.3-1.0), whereas both low to moderate and heavy smoking increased the risk of very preterm birth due to all other mechanisms (aOR between 1.6 and 2.8). Conclusion These data from the Epipage study show that maternal smoking during pregnancy is a risk factor for very preterm birth. The impact of maternal smoking on very preterm birth appears to be complex: it lowers the risk of very preterm birth due to gestational hypertension, but increases the risk of very preterm birth due to other mechanisms. These findings might explain why maternal smoking is more closely related to preterm birth among multiparous women than among nulliparous women.

Determinants of preterm birth: Pelotas, Rio Grande do Sul State, Brazil, 2004 birth cohort

“…The literature shows a modest, dose-dependent association between smoking, preterm birth and stillbirth 15,20 . This effect may be stronger for early preterm delivery (< 35 weeks) than for late preterm birth 21,22 . Because smoking during pregnancy has become increasingly associated with low socioeconomic position, residual confounding is a possible explanation for positive findings 15 .…”

Weakening and Rupture of Human Fetal Membranes – Biochemistry and Biomechanics

“…Decidual hemorrhage/abruption is also highly associated with PPROM (Harger et al, 1990;Salafia et al, 1995). Additional risk factors include advanced maternal age, primiparity, (Ladfors et al, 2000) smoking, (Burguet et al, 2004) short cervical length structural abnormality of chorioamniotic membranes (Stuart et al, 2005), and PPROM with preterm birth in a previous pregnancy (Ladfors et al, 2000;Lee et al, 2003;Shen et al, 2008). African American women are at higher risk of PPROM than Caucasian women (Goldenberg et al, 1996a), which might be due to racial differences in the regulation of promoter activity of pro-inflammatory cytokines and MMPs (Simhan et al, 2003;Ferrand et al, 2002).…”

Tobacco and pregnancy: Overview of exposures and effects

“…Preterm birth (delivery at 33-36 weeks gestation), which occurs in 5-10% of all births in Western countries (Meis et al, 1995) and very preterm birth (delivery at \33 weeks gestation), which occurs in 1-2% of births in developed countries (Burguet et al, 2004) are major causes of neonatal morbidity and mortality. A dose response relationship between maternal smoking and the incidence of preterm birth has been repeatedly observed (Kyrklund-Blomberg and Cnattingius, 1998;Fantuzzi et al, 2007;Nabet et al, 2007).…”