Effects of maternal smoking on body size and proportions at birth: a register-based cohort study of 1.4 million births

Abstract

ObjectivesThe aim of our work was to analyse the effect of maternal smoking on body size and body proportions of newborns when the mother had smoked only during the first trimester, in comparison with continued smoking after the first trimester. Furthermore, we have evaluated how growth restriction associated with maternal smoking contributes to changes in body proportions.DesignRegister-based cohort studySettingMaternal Exposure (MATEX) cohort identified from the Finnish Medical Birth Register.ParticipantsSingleton births without congenital anomalies and missing data (1.38 million) from 1 January 1991 to 31 December 2016.MethodsLogistic regression was used to quantify the effect of maternal smoking, stratified by the maternal smoking status.Outcome measuresBody proportions indicated by low brain-to-body ratio (defined as <10th percentile); high ponderal index and high head-to-length ratio (defined as >90th percentile); small body size for gestational age at birth (defined as weight, length or head circumference <10th percentile) and preterm birth (<37 weeks) and low birth weight (2500 g).ResultsContinued smoking after the first trimester was associated with high ponderal index (OR 1.26, 95% CI 1.23 to 1.28), low brain-to-body ratio (1.11, 1.07–1.15) and high head-to-length ratio (1.22, 1.19–1.26), corresponding with absolute risks of 22%, 10% and 19%, respectively). The effects were slightly lower when smoking had been quit during the first trimester. Similar effects were seen for the body size variables and low birth weight. Preterm birth was not associated with smoking only during first trimester.ConclusionsMaternal smoking, independent of smoking duration during pregnancy, was associated with abnormal body proportions resulting from larger reduction of length and head circumference in comparison to weight. The effects of having quit smoking during the first trimester and having continued smoking after the first trimester were similar, suggesting the importance of early pregnancy as a sensitive exposure window.

Smoking and Smoking Cessation in the Risk for Fetal Growth Restriction and Low Birth Weight and Additive Effect of Maternal Obesity

“…In recent decades, attention has been paid to factors impacting the fetal environment as important elements of the concept of the development of health and disease (DOHaD) [1,2]. Adverse birth outcomes have been associated not only with increased perinatal mortality and offspring neurodevelopmental disorders but also with long-term adverse health effects [1,3]. In particular, abnormal (low and high) birth weight has been associated with a higher risk of "non-communicable diseases" such as obesity/overweight or diabetes mellitus and cardiovascular diseases [1][2][3][4][5].…”

“…Cigarette smoking is a modifiable environmental factor associated with many adverse pregnancy results, such as low birth weight, preterm birth, and higher newborn mortality [2,4,[6][7][8]. Tobacco smoke contains several thousand chemicals that can be harmful to the placenta and pass through the placenta to the fetus [2,3]. An important component of tobacco smoke, nicotine can interfere with the physiological transformation of spiral arteries and increase the risk of pregnancy complications [4,9].…”

Chained Risk Assessment for Life-Long Disease Burden of Early Exposures–Demonstration of Concept Using Prenatal Maternal Smoking

“…The prevalence of PTB and LBW with corresponding risk estimates for the associations with maternal smoking were identified from the MATEX birth cohort [15]. The prevalence of childhood overweight and obesity were estimated from Finnish population growth curves based on the WHO definition of overweight and obesity (Table 1) [28].…”

“…Prenatal maternal smoking is a known early exposure associated with adverse birth outcomes [14,15]. Despite public health efforts, maternal smoking remains to be prevalent with 14% of all newborns exposed in Finland in 2015 [16].…”

“…Emerging evidence is suggesting DNA methylation as a mechanism for the effect of maternal smoking on birth weight [20]. Furthermore, maternal smoking during early pregnancy is causing disproportionate growth restriction, demonstrating differences in susceptibility of organ systems for adverse effects [15]. Growth restriction is evident as early as during the first trimester ultrasound scans [21].…”