Nicotine
is one of the major components in tobacco smoke, and it can cross the placenta.
It enters the fetal circulation and accumulates in the fetal compartments from
as early as seven weeks of gestation, even with passive smoking. Elevated fetal
carbon monoxide levels may result in hypoxia due to reduced availability of
hemoglobin for oxygen transport. Exposure to hazardous substances in cigarette
smoke could lead to adverse pregnancy and birth outcomes. In particular,
maternal nicotine exposure is associated with many adverse fetal, placental,
and postnatal health outcomes, including both shortterm and long-term
complications. Despite increased awareness of the harmful effects of smoking
during pregnancy, approximately 20% of women continue to smoke throughout
pregnancy in the world. Reducing smoking in pregnancy is a global public-health
priority. We recommend clinical and public-health strategies aimed at the
primary and secondary prevention of tobacco exposure for fetuses and children.
The World
Health Organization (WHO) estimates that the prevalence of smoking is
approximately 22% of women in developed countries and 9% of women in
underdeveloped countries. The 2011 Pregnancy Risk Assessment Monitoring
System (PRAMS) polled women from 24 states in the US. The self-reported data
showed that about 23% of reproductive-aged women smoked during the three months
before pregnancy, and about 10% of women smoked during the last three months of
pregnancy. About 55% of women who smoked before pregnancy reported they had
quit smoking by the last three months of pregnancy. The highest prevalence of
those smoking during the last three months of pregnancy (15-16%) was in the age
groups of 24 years and younger (Figure 1). A strong correlation has been
seen between maternal smoking during pregnancy and young age, unmarried status,
and being from a low socioeconomic status.
The
Centers for Disease Control and Prevention’s (CDC) PRAMS showed the trends of
smoking three months before pregnancy, during, and after pregnancy data from 40
states in the US from 2000 to 2010. During this decade, the prevalence of
smoking in the three months before pregnancy remained unchanged at about one in
four women. However, the prevalence of smoking declined in the last three
months of pregnancy from 13.2% to 11.6% and after delivery from 17.8% to 16.6%.
The data showed that 40% of women who quit smoking during pregnancy relapsed
within six months after delivery.
Other
parts of the world had a greater decrease in smoking for women. Dias-Dame et
al., conducted population-based survey in Brazil, data of 7,572 women showed
that the prevalence of smoking before pregnancy decreased from 28% in 2007 to
22% in 2013, and the prevalence of smoking during pregnancy decreased from 22%
in 2007 to 18% in 2013. In Australia, the prevalence of smoking in
pregnancy in New South Wales declined from 22.1% in 1994 to 13.5% in 2007. The
largest decrease in smoking in pregnancy rates was among the highest
socioeconomic group, and smaller declines were observed among teenage and
remote rural mothers.
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