Effects of tobacco smoking and pregnancy: Relationship to Preterm Birth

Tobacco Smoking & Preterm Birth

A comprehensive body of research demonstrates a dose-dependent relationship between smoking tobacco and preterm birth and low birth weight (LBW). In other words the more cigarettes smoked the higher the chance of having a preterm birth. Smoking appears to be primarily associated with an increased risk of very preterm birth by increasing the risks of preterm labour, preterm premature rupture of membranes (PPROM), and bleeding in pregnancy. In industrialized countries, maternal cigarette smoking during pregnancy accounts for about 30%–40% of small for gestational age (SGA) births

(Fantuzzi et al., 2007; Kyrklund-Blomberg, Granath, & Cnattingius, 2005)

Data collected in Australia from 2003 show that the risk of preterm birth was 60% higher in infants of mothers who smoked during pregnancy than in infants of mothers who did not smoke. It is estimated that maternal smoking is responsible for 15% of all preterm births, 20-30% of all low birth weight (LBW) infants, and increases neonatal mortality by 30%. Smoking is mainly associated with an increased risk of very preterm birth by increasing the risks of preterm labour, PPROM, and bleeding in pregnancy. The nicotine and carbon monoxide in cigarettes are vasoconstrictors and are associated with placental damage and decreased blood flow, which can lead to fetal growth restriction. The placenta can also be affected by nutritional adversities such as lower serum folate and ascorbic acid levels, which are found in pregnant smokers.

(Basso, Wilcox, & Weinberg, 2006; Clausen, Jorgensen, & Ottesen, 1999; Dew, Guillory, Okah, Cai, & Hoff, 2007; Kyrklund-Blomberg, et al., 2005; Laws, Grayson, & Sullivan, 2006)

Rates of smoking in Australia

In Australia the percentage of women who smoked while pregnant ranged from 12.8% in both New South Wales and the Australian Capital Territory to 28.0% in Tasmania. There was no data available for Victoria.

• Overall, 16.6% of women in these states and territories smoked during Pregnancy
• The average age of mothers who smoked during pregnancy was 26.9 years
• Teenage mothers accounted for 11.4% of all mothers who reported smoking during pregnancy

{Laws, 2009 #1083}

Aboriginal Women

• Over half of the Aboriginal and Torres Strait Islander mothers reported smoking during pregnancy (51.8%)
• Aboriginal or Torres Strait Islander mothers accounted for 14.6% of mothers who smoked during pregnancy

{Laws, 2009 #1083}

Rates of smoking in Canada

2005: In Canada the percentage of women who smoked while pregnant ranged from 9.7% and 10.3% in British Columbia and Ontario, respectively, to as high as 59.5% in Nunavut and 32.8% in the Northwest Territories.

• Overall in 2005, 13.4% of women in Canada reported smoking during their pregnancy.
• In 2000-2001 the rate of mothers who reported smoking during their pregnancy was 17.7%.
• In 2005, young mothers were more likely to report smoking. 37.2% of mothers who were under 20 years of age smoked during their pregnancy, compared with 9.0% of mothers who were 40 years of age or older.
• Mothers under 20 years accounted for 3.0% of all mothers who reported smoking during pregnancy

Public Health Agency of Canada. Canadian Perinatal Health Report, 2008 Edition. Ottawa, 2008.