Pre y dolarización

Matemal reports o f smoking were validated by cotinine assay o f matemal saliva and infant urine samples obtained at time o f test. Generally, there was good concordance between matemal reports o f smoking and cotinine assay o f the saliva and urine samples. However, five infants (2 AGA and 3 SGA) were re-classified into the smoking category as matemal salivary cotinine concentrations ranged from 20.8 to 434.6 ng.mL’’ and were consistent with values from active smokers (> 1 5 ng.mL*’) (Figure 4.6) (McNeill et al. 1987; Jarvis et al. 2000). Thus, following re­ classification o f the five infants into the smoking category, cotinine levels were negligible in the non-smoking group while higher levels were observed in the smoking category in both saliva and urine samples (Table 4.5). Seven mothers who reported smoking after eight weeks’ gestation and/or postnatally and who were therefore classified as ‘smokers’, were found to have salivary cotinine < 2 ng.mL'% suggesting they were ‘light’ smokers (Figure 4.6).

Table 4.5 Summary of cotinine results according to validated maternal smoking status^

Non-smoking Smoking Matemal salivary cotinine^ 0.2 (0.1 - 0.7) 198.1 (77.2 - 357.5) Infant urinary cotinine^ 1 -5 (0.6 - 2.5) 11.9 (5.6 - 30.8)

'Data shown as median (inter-quartile range) ng.mL’* ^ n = 100; n = 74 respectively

Figure 4.6 Cotinine levels of maternal saliva and infant urine classified according to validated maternal smoking status

Salivary cotinine 15ng.mL' 2001

i

1

Mother’s smoking status + light smoker r e -c la ssifie d as sm o k er

I_s

Maternal salivary cotinine (ng.mL'‘)

Note: Logarithmic scales; only three mother-infant pairs of the five re-classified are shown as two infant urine samples were unavailable. Only five of the seven light smokers are shown, for the same reason.

W h ile maternal reports o f sm ok ing w ere broadly reliable, there w a s considerable

overlap in infant cotin in e v alu es b etw een infants w h o w ere and w ere not exp o sed to

maternal sm oking. In addition, from the w id e range o f infant urinary cotin in e lev els

observed am on g infants not exp o sed to maternal sm ok in g, it w as clear that there

w ere other significant sources o f tobacco sm ok e exp osu re ev en at this you ng age

(Figure 4.6).

Table 4.6 Cotinine levels according to SGA/AGA classification and maternal smoking status^

Non-smoking Smoking

SGA AGA SGA AGA

Maternal salivary cotinine^

Infant urinary cotinine*

0.3 ( 0 .1 - 0 .7 ) 1.5 ( 0 .8 - 2 .4 ) 0.1 ( 0 .1 - 0 .6 ) 1.6 ( 0 .4 - 2 .5 ) 226.2 (9 7 .7 -4 3 5 .7 5 ) 15.3 ( 7 .0 - 3 0 .8 ) 182.0 ( 3 1 .4 - 305.25) 9.2 (4 .2 - 3 1 .3 )

'Data shown as median (inter-quartile range) ng.mL*' ^ n = 38; n = 62; n = 38; n = 36 respectively;

^ n = 32; n = 57; n = 35; n = 31 respectively.

When cotinine concentration was compared according to birthweight classification and smoking status, salivary and urine cotinine levels were similar in the two non­ smoking groups. However, levels observed in the SGA infants exposed to maternal smoking tended to be higher when compared to the AGA smoking group, though this difference was not significant.

Figure 4.7 M aternal salivary cotinine levels according to num ber of cigarettes smoked 1000 5 0 0 100 5 0 10 5 .5 * .1 $ .05 .01 .0 0 5 .001 $1 4- - I - -h + ::

$

Maternal smoking status

“1“ s m o k e d in p r e g n a n c y & p o s tn a ta lly ( n = 6 2 ) s t o p p e d s m o k in g < 2 0 w but s m o k e d P /N ( n = 4 ) ® s t o p p e d s m o k in g < 2 0 w g e s ta tio n ( n = 4 ) 15 20

N um ber o f cigarettes sm oked per day

2 5 3 0

Note: Logarithmic scale; Definition of abbreviation: P/N = postnatal; Maternal salivary cotinine not available for 3 mothers who stopped smoking by 20 weeks gestation but continued to smoke postnatally and 2 mothers who stopped smoking by 20 weeks gestation, hence only 7 and 4 data points respectively are shown.

Figure 4.7 shows maternal salivary cotinine level according to self reported smoking habit at time o f test. A wide range of cotinine levels (from 0.7 - 722 ng.mL"') was observed among those who reportedly smoked < five cigarettes per day. Thus while maternal report of smoking status was broadly reliable with only 5/110 (4.5%) self reported non-smokers probably being active smokers, maternal report o f the amount smoked correlated poorly with the biochemical assay o f exposure. Additionally, Figure 4.7 shows that, above 4 cigarettes per day, the number o f cigarettes smoked tended to be rounded to multiples of five.

4,4.4.1 Association between infant cotinine levels and method o f feeding

Figure 4.8 Cotinine levels according to method of infant feeding at time of test g> o 0 •c 1 15 ng.mL" 200 00 50 40 30 20 10 5 4 3 2 1 5 ' 4 ' 3 2 ' 1 A_ .0001 .001 .01 1 10 100 1000 ■ Breast/bottle ^ Bottle ^ Breast

Maternal salivary cotinine (ng.mL'')

In Figure 4.8 infant’s tobacco smoke exposure, as reflected by maternal salivary and infant urinary cotinine levels, was classified according to maternal report of infant feeding method. Among mothers who did not smoke, as represented by most o f the data points to the left of the cotinine cut-off level for maternal saliva (15 ng.mL'’), infant cotinine levels were varied but there was no clear pattern according to feeding method. By contrast, among mothers who smoked, as represented by all the data points to the right o f this threshold, infant urinary cotinine was highest among infants who were breast-fed and lowest in those who were bottle-fed, with those who were breast and bottle-fed having intermediate values.

Infant and maternal cotinine levels from mothers who smoked are presented in Table 4.7 according to infant feeding method at time o f test. Women who bottle-fed their

infants were more likely to smoke > 1 0 cigarettes per day. Hence, mean salivary cotinine levels were also higher in the mothers who bottle-fed their infants (Table 4.7). In contrast, infant urinary cotinine levels were, on average, higher in the breast­ fed group, probably reflecting additional ingestion o f cotinine via breast milk.

Table 4.7 Cotinine levels from mothers who smoked and infant feeding method at time of test^

Infant feeding method Breast Breast/Bottle Bottle n = 24 n = 15 n = 39 Smoked > 10 cigarettes/day 5 (21%) 3 (20%) 15 (38%) Maternal salivary cotinine 1 4 6 ( 3 5 - 2 1 8 ) 2 1 7 ( 1 0 2 - 3 7 2 ) 2 5 3 ( 8 9 - 3 9 1 ) Infant urinary cotinine 32 (8 - 118) 17 (9 - 32) 8 (5 - 16)

‘Data shown as median (inter-quartile range) ng.mL‘‘ for continuous and n (%) for categorical variables.

Thus, among infants whose mothers smoked, median infant urinary cotinine was four times higher in infants who were exclusively breast fed, relative to those infants fed only by bottle. By comparison, median infant urinary cotinine level was only twice as high in those who were breast and bottle-fed.

4,4,4,2 Association between cotinine levels and sources o f tobacco smoke exposure

Table 4.8 Infant urinary cotinine levels according to maternal and household exposure^

No exposure Household Mother exposure Mother & household exposure only only exposure (n = 56) (n = 23) (n = 15) (n = 46) Infant urinary 1.4 1.8 8.4 15.3 cotinine ( 0 .6 - 2 .5 ) ( 0 .8 - 4 .5 ) ( 3 .7 - 2 4 .1 ) (6 .9 - 3 2 .6 )

'Data shown as median (inter-quartile range) ng.mL'*

In order to assess the influence of other sources o f tobacco smoke exposure in the infant, infant urinary cotinine levels were calculated according to maternal smoking and other household exposure (Table 4.8). Infant urinary cotinine levels were negligible in the group with no exposure and minimally elevated in the 23 infants who were exposed to other household smokers (mother being a non-smoker). By contrast, for infants who were exposed to maternal and other household smokers, there was a more marked increase in their urinary cotinine levels when compared to those who were only exposed maternal smoking.

Table 4.9 Cotinine levels according to maternal and household exposure^

No exposure (n = 56) Household exposure only (n = 23) Mother exposure only (n = 15)

Mother & household exposure (n = 46) Infant urinary 1.4 1.8 8.4 15.3 cotinine ( 0 .6 - 2 .5 ) ( 0 .8 - 4 .5 ) ( 3 .7 - 2 4 .1 ) (6 .9 - 3 2 .6 ) Maternal salivary 0.1 0.4 132.6 266.3 cotinine ( 0 .1 - 0 .6 ) ( 0 .1 - 1 .2 ) (21 - 3 4 3 ) (1 5 8 - 3 9 1 ) Smoked > 1 0

cigarettes per day 4 (29%) 19 (42%)

Data shown as median (inter-quartile range) ng.mL' for continuous variables and n (%) for categorical variable.

The same pattern was observed for maternal salivary cotinine, suggesting that mothers who are active smokers may be exposed to passive smoke exposure from other household members as well. However, some o f the differences noted may be due to the fact that mothers who smoked and lived with other smokers within the same household tended to smoke more than those who lived with a non-smoker. In households where the mother is the only smoker, the median number o f reported

cigarettes smoked was three per day (range 1 - 20) and in households where there was at least one other smoker (excluding the mother), the median number of cigarettes smoked by the mother was reported to be 10 per day (range 1 - 30).

Thus, relative to infants who were not exposed to tobacco smoke, median infant urinary cotinine levels were on average six times higher among infants who were exposed to maternal smoking only and 11 times higher when exposed to maternal and other household smokers.