SMOKING IN PREGNANCY
The first suggestion that smoking during pregnancy
might
harm the child was made by Knopf as long ago aciL
1929. Since.that
time, there have been many studies and, as the
anti-smoking
attacks have inereasecd in luitensity, so t*oo
havc tho studics of
the effpetR of smokina bv the mother on the unborn
child. An
editorial in 'Lancet' in 1974 summarised the
literature well to
that time and is appended. It seems a balanced
article,
mentioning the counter-argxnents, particuIRrly
those of
Yerushalmy, which it dismisses, and relegating to
the status of
an "interesting speculation" the suggestion that
"passive smoking"
by young babies is harmful to their health.
The 'Lancet' editorial is primarily aimed at an
assessment
cLf.tbe risks of "passive smoking., on which it
concludes that,
apart from a very small minority of especially
sensitive, and
possibly allergic, people, ".for most adult
non-smokers, tobacco
smoke pollution is at worst.a source of.annoyance
and temporary
irritation". But it returns to the theme of damage
to the unborn
child at the end.
Siiice-this review, one potentially significant
piece
of. work has 'been published. Dr.- Boddy..and his
eo-w6rkers at
Oxford have developed a technique, based on-the
use of an ultra-
son ic scanning aparatus, for observing the foetus
in.~ Iter6.
e- so'4'iat ar,6uiid-t~_~S Weeks'
They. -found that- n*oirm-al. hea'Itbylo Lu
gestation made,. "breathing majioeuvres" for part
of the time..
V
varying with ,the tii~e.,,of'day',.'rising from
45%-aetivity in the
early bouts of the -morting to 90% in the early
evening..
Presumably, thla is related to the" development of
musege tone..in
the chest-prior-to birth, so~that the
new-born-infant will. have
functloiiing muscles. -when these are needed.
for--respit'atiall.
The Oxford group--rep.orted,ii.vBrit. Med.' J.
(1975,
Sth March,- pp~-.-5.52_..3Y their observations on
the. foetuses 0t
18., women, who-smokpd,,to varyIng degrees, during
pregnancy.
n
Se u;lu, so oV_.t"._.variatL4n jJd_- th-e.
pmqPnr~t qxv
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same time of day. The foetuses were observed for a
control
period of about J to I hour and then the mother
was allowed to
smoke two cigarettes. In every case, there was a
fall in the
percentage of time that foetal breathing movements
were observed,
whieh was highly signif..'scant statit;ticaliy. On
average, the
change was from 65% activity to 50% in 5 minutes
and to a minimum
of 45% in about 35 minutes. The rate returned to
normal about
1-hour after smoking. It should be noted that the
size of this
transient change is less than the normal diurnal
variation in
the incidence of foetal breathing movements-
Boddy et al. speculate as to the cause of this
change
and advance a number of plausible expla-nations:-
reduction in-maternal placental blood-flow
placental transfer of some tobacco smoke
constituent
e.g. nicotine or carbon monoxide
They report some preliminary observationa with
cigarettes-
not containing nicotibe, which suggest that
smoking these does..
not lead to an impairment of foetal breathing
movements.
The work at Oxford is 'being fGillowed up,in
Sweden by
Dr. Gennser at Malmd, supported'.by the Swedish
Tobacco Co-and
_plies of a.non-tobacco herbal
we --have - a---,isted--bY-- sending - sup
cigarette (Honeydew-Special), v4lch contains,,no
nicotine... s
not known,whether Gennser confirms the'-puggestion
by Boddy-.and his
group Ihat nicotine, rather than carbon monoxide,
is responsible
for repressing foetal breathing movements.
.-Boddy~-et unable to relate their- -observations
o f-
the acuteeffect of cigarette.smoking to the.1ong
term,
-i~il 'iepoils, 001AL 6ut" 11"lit
epidemiologi
tontetits of.. th~
such as'reduaed oxygp~ and sugar. placenial blood
circulation, which~might be expected to bave
adVe~rse effee-ts on,
the unborn child, also reduce footal breathing
movements. While
it remains: speculation, it :Ls -argument
that,qigarette
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The Lancet editorial,referred to earlier,
focusses: on
the effect of smoking on -birthweight and
perinatal mortality, for
which it appears to accept the estimate of 1,500
deaths per annum
in the TI.K. Smoking i.p nlleged to lead to
retnidcd intTaUtcrinc
growth, so that babies are lighter at birth and
consequently,
smaller. It has recently been pointed out that
small birth size
does not necessarily make for an easier labour,
because-t-he baby-Is
head remains the same size and the lighter weight
merely implies
an undernouritihed body. The- infant is,
therefore, more vulnerable
in its early days,
Donovan has recently drawn attention to the
possibility
that the reduoed weight at birth-may ha-ve more
permanent effects.
For example, it has been claimed by. Butler and
Goldstein that on
re-examining at the ages-of tmveli and eleven,
those children whose
birth weights were measured in an earlier survey
in 1958, they
were found to be Gb=tcr and. behind in th-eir
reading and
mathematical ability.. This Is a controversial
finding in that
the interaction of maternal smoking- and
educational ability with
social class, number of elder siblings and the
mil'ieu in vALLch
the children are raised' is complicated. Moreover,
there is. a
greater difference in reading ability between
children in extremes
social classes than was shown.between the,
children of smoking and
non~aanlohing mothers-.
Other studies have been made of the relationship
between
,moking and congenital abnormalities, but theso
have,411 pkaved
to beneg4tive,. except fQr'the claim that
.16-mokers," infants have.-
a higher incidence of congenital heart disease.
(Note: Throughout all, the atUdles sur"Ved,
-at-tentiwilig-
focussed on smoking byAhe pregnant Voma In
thefarea of
congen~ital.abnormality, it is a possibility that
someone
may iiiempt to link thi-s. to smokling. b_y the f
ather- With-,
uconseqt~ent modification in the genetic makeup of
the -sjperm.
t enic
Animal experiments attempting-to demonstrat mu ag
7 7
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SutmD:xry
The (Aalm thaL sinuking during pregnancy leads to
smaller
babies and increases the ri8k of peritiatal
mortality, eSLimated
at 1,500 infant deaths a year in the U.K., appears
to be sustained.
It is possible. that this is due to a reduction in
placental
blood flow or to the transfer to the foetal
circulation of some
smoke component absorbed by the mother.
Observation of foetal
breathing movements and their suppression
following-maternal
smoking lends some substance to the explanation.
Tentative
indications are that the component 9aZ be
nicotine, but this
requires substantiation.
Risk to the new-born infant by passive smoking
appears
more remote.
Longer term effects on children due to smoking by
pregnant mothers is more controversial, as are
claims that
congenital abnormalities are re-lated.to smoking
during pregoandy.
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