Every single cigarette a woman smokes affects her health,
her pregnancy, and her baby’s health.
Smoking is the most important modifiable cause of poor pregnancy
outcome among women.
A systemic absorption on toxins occurs whilst smoking when
pregnant. Nicotine, carbon monoxide and other toxic constituents
of tobacco smoke cross the placenta readily, having a direct
effect on the oxygen supply to the foetus, and the structure
and function of the umbilical cord and placenta. A number
of tobacco smoke constituents that cross the placenta are
known carcinogens. Nicotine has a direct effect on foetal
heart rate and breathing movements. Nicotine is also found
in the breast milk of women who smoke.
Spontaneous abortions and complications of pregnancy and
labour occur more frequently in smokers. Smokers have a higher
risk of ectopic (tubal) pregnancy and have a greater tendency
to deliver pre-term. Women who smoke during pregnancy have
a 25 to 50% higher rate of foetal and infant deaths compared
Exposure by the mother to workplace passive smoking and paternal
smoking has also been associated with lower birth-weight,
a higher risk of perinatal mortality and spontaneous abortion,
particularly in the second trimester of pregnancy.
Maternal smoking exerts a direct growth retarding effect
on the foetus, resulting in a decrease in all dimensions including
length and circumference of chest and head. Infants of smokers
weigh on average 200 grams less than the infants of non-smokers,
and smokers have double the risk of having a low birth-weight
Maternal smoking predisposes the child to respiratory illness.
Parental smoking has been linked with decreased pulmonary
function and asthma in children.
The increased risk of reduced respiratory function, and increased
risk of Asthma and Sudden Infant Death Syndrome (SIDS) is
most marked in children of mothers who smoke heavily (more
than 10 cigarettes per day).
Smoking behaviour characteristics amongst pregnant women
and new mothers suggest that:
women who smoke during pregnancy will continue to smoke
of those who do not smoke during pregnancy many will
start/resume smoking postnatally
few mothers who smoke during pregnancy will then stop
Evidence suggests that pregnant women need to quit smoking
or reduce consumption during the first half of pregnancy to
reduce the risks. Non-smoking expectant mothers should avoid
exposure to cigarette smoke during their pregnancy in order
to avoid many respiratory health problems in their child’s
An increased risk of SIDS when babies are exposed to cigarette
smoke has been found in over 30 case-control and cohort studies
(Mitchell 1995, Golding 1997). This finding is consistent
over time and place. Many studies have reported a dose-response
A recent case-control study in the UK (Blair et al 1996)
carried out on families with infants born 1993-1995, since
the change in sleeping position was promoted, found that the
incidence of smoking during pregnancy was greater in mothers
of 195 SIDS cases (63%) than in mothers of 780 controls (25%)
(AOR 2.1 (1.24, 3.54)). If fathers were smokers then there
was an independent additive increase in the risk of SIDS (AOR
2.4 (1.48, 4.22)).
If parents smoked in the house after birth, then there was
an independent additive increased risk of SIDS (AOR 2.93 (1.56,5.48)).
The population attributable risk from smoke of 61% is higher
than the 33% reported for smoking prior to the reduction of
prone sleeping (Mitchell 1995).
Reprinted with permission from the ‘Reducing the
risk of Sudden Infant Death Syndrome (SIDS)’ booklet.