Supplementary Materials
The impact of maternal smoking during pregnancy on depressive and anxiety symptoms in
offspring
Supplementary Methods
MOBA Study
Detailed information regarding the Norwegian Mother and Child Cohort (MoBa) can be found
at
(http://www.fhi.no/eway/default.aspx?pid=240&trg=Main_6664&Main_6664=6894:0:25,7372:
1:0:0:::0:0) and Magnus et al(1). For the included cohort, participation rates were 38.7% of
those invited. In a comparison performed on data acquired in MoBa between 2000 - 2006 and
data from the Norwegian Medical Birth Registry, maternal participants in MoBa were more
likely to be older, less likely to be single, have lower parity, have lower rates of previous
stillbirths and less likely to suffer maternal asthma(2). In addition, MoBa participants were
more likely to be non-smokers, more likely to use folic acid, and less likely to suffer from
gestational diabetes and placental abruption.(2) Study response rates in our cohort were
94.9% for questionnaire 1 (early pregnancy), 91.0% for questionnaire 3 (late pregnancy),
72.5% for questionnaire 5 (18 month follow up), 58.5% for questionnaire 6 (36 month follow
up) and 53.0% for questionnaire 7.
Instruments and Measures
The administrating committee of MoBa provides detailed documentation explaining the
rationale behind choice of all instruments used in the study. In regards to childhood behaviour
assessment, mothers reported symptoms by answering questions taken from the Childhood
Behaviour Checklist (CBCL)(3). The CBCL is a commonly used tool to assess child
behaviour, and can be divided into subscales including “emotionally reactive”,
“anxious/depressed”, “somatic complaints”, “withdrawn”, “sleep problems”, “attention
problems” and “aggressive behaviour”, with the first 4 representing “internalising symptoms”
and the last two categories representing “externalising symptoms”. The CBCL requires
participants have a minimum fifth grade reading level. MOBA condensed the larger CBCL
into a shorter 25-question version, of which the relevant questions for this study have been
mentioned in the main text. At the 18-month questionnaire, internalising symptoms were
assessed using 5 items from the CBCL internalising scale. At the 36-month questionnaire,
internalising symptoms were assessed using 9 items from the CBCL internalising scale. At
the 5-year questionnaire, internalising symptoms were assessed using 11 items from the
CBCL internalising scale. Clark and Watson(4) argue the mean inter-item correlation as a
useful index of internal consistency for such scales, and recommend that this should be in the
range 0.15 to 0.20 for broad constructs. Mean inter-item correlation for the CBCL items was
0.14 at 18 months in the current sample, 0.13 at 36 months in the current sample, and 0.16 at
5 years in the current sample. Factor analysis of the scales demonstrated that scale items
were best explained by one factor at each time point (results available on request). The CBCL
has been shown to possess good predictive validity in the Norwegian population(5), with the
Norwegian translation performed by Nøvik(5, 6) used in this study.
Web Results
Study Attrition and Missing Variable Analysis
Attrition: Multivariate logistic regression showed that attrition at late pregnancy was predicted
by low maternal educational level (OR = 0·93, p <·01), high levels of depression in early
pregnancy (OR = 1·38, p <·01), parity (OR = 1·09, p <·01), and smoking in early pregnancy
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(OR = 1·40, p <·01). Attrition at 18 months was related to low maternal educational level (OR
= 0·87, p <·01), maternal depression in early pregnancy (OR = 1·28, p <·01), low maternal
age (OR = 0·97, p <·01), parity (OR = 1·11, p <·01), low gestational age at birth (OR = 0·93, p
<·01), and to smoking in early pregnancy (OR = 1·26, p <·01). Paternal smoking, maternal
smoking in previous pregnancies, and maternal alcohol consumption in early pregnancy were
not related to attrition in late pregnancy or 18 months. Attrition at 36 months was predicted by
maternal education (OR = 0·86, p<·01), maternal depression in early pregnancy (OR = 1·25,
p <·01), smoking in previous pregnancies (OR = 1·09, p <·01), low maternal age (OR = 0·98,
p <·01), parity (OR = 1·13, p <·01), low gestational age at birth (OR = 0·95, p <·01), and to
smoking in early pregnancy (OR = 1·19, p <·01). Paternal smoking and maternal alcohol
consumption in early pregnancy did not predict attrition at 36 months. Further, in these
multivariate analyses, internalizing problems at 18 months did not predict attrition at 36
months. Attrition at 5 years was predicted by low maternal educational level (OR = 0·94, p
<·01), maternal depression in early pregnancy (OR = 1·22, p <·01), smoking in previous
pregnancies (OR = 1·14, p <·01), low maternal age (OR = 0·99, p <·01), low levels of
maternal alcohol consumption in early pregnancy (OR = 0·91, p <·01), low gestational age at
birth (OR = 0·97, p <·01), and smoking in early pregnancy (OR = 1·49, p<·01). Internalizing
symptoms at 36 months did not predict attrition at 5 years in these multivariate analyses.
Missing information on internalizing symptoms and smoking: Missing information on maternal
smoking in early pregnancy was related to high educational level (OR = 1·15, p <·01), low
age (OR = 0·97, p<·01), high alcohol consumption (OR = 1·29, p <·01), and parity (OR =
1·16, p <·01). At 18 months, 5274 women returned the questionnaire with missing information
on internalizing problems. Multivariate logistic regression showed that this was predicted by
low maternal educational level (OR = 0·75, p <·01), high maternal alcohol consumption in
early pregnancy (OR = 1·78, p <·01), and smoking in early pregnancy (OR = 1·91, p <·01). At
36 months, 407 women returned the questionnaire with missing information on internalizing
symptoms, and 95 women did this at 5 years. This was not predicted by any of the
aforementioned variables or by internalizing symptoms at the previous questionnaires in
multivariate logistic regression analyses.
Web Table 1: Descriptive statistics of internalising symptoms and confounding factors
Internalising 18 months
(Range 1-3)
Internalising 36 months
(Range 1-3)
Internalising 5 years
(Range 1-3)
Maternal depression in early pregnancy
(Range 1-4)
Maternal age
Gestational age at birth
Mean (SD)
1.27 (0.25)
N Available (%)
69946 (65.1%)
N Missing (%)
37433
(34.9%)
1.25 (0.22)
57143 (53.2%)
1.16 (0.19)
19778 (18.4%)
1.26 (0.40)
99533 (92.7%)
50236
(46.8%)
87601
(81.6%)
7846 (7.3%)
29.8 (4.6)
39.34 (2.26)
101764 (94.8%)
106440 (99.1%)
5615 (5.2%)
939 (0.9%)
Web Table 2: Descriptive statistics of potential confounding variables
N (% total)
Maternal Education
≤9 years education
2782 (2.6%)
2
1-2 years high schooling
3 years schooling
1-4 college/university
>4 years
college/university
Missing data
4944 (4.6%)
26854 (25.0%)
39388 (36.7%)
22579 (21.0%)
Never
<1 episode per month
1-3 episodes per month
<1 episode per week
2-3 episodes per week
4-5 episodes per week
6-7 episodes per week
Missing data
74702 (69.6%)
8615 (8.0%)
1995 (1.9%)
429 (0.4%)
61 (0.1%)
7 (0.0%)
15 (0.0%)
21555 (20.1%)
0
1
2
3
4+
Missing data
47515 (44.2%)
38188 (35.6%)
16443 (15.3%)
3610 (3.4%)
1132 (1.1%)
492 (0.5%)
Yes
No
Missing data
25039 (23.3%)
76079 (70.9%)
6261 (5.8%)
10832 (10.1%)
Maternal Alcohol
Consumption
Maternal Parity
Paternal Smoking (early
pregnancy)
Web References
1.
Magnus P, Irgens LM, Haug K, Nystad W, Skjaerven R, Stoltenberg C. Cohort profile:
the Norwegian Mother and Child Cohort Study (MoBa). International journal of epidemiology.
2006 Oct;35(5):1146-50. PubMed PMID: 16926217. Epub 2006/08/24. eng.
2.
Nilsen RM, Vollset SE, Gjessing HK, Skjaerven R, Melve KK, Schreuder P, et al.
Self-selection and bias in a large prospective pregnancy cohort in Norway. Paediatric and
perinatal epidemiology. 2009 Nov;23(6):597-608. PubMed PMID: 19840297. Epub
2009/10/21. eng.
3.
Achenbach TM. Manual for the child behavior checklist/2-3 and 1992 profile.
Burlington, VT: Department of Psychiatry, University of Vermont; 1992. xi, 210 p. p.
4.
Clark LA, Watson D. Constructing validity: basic issues in objective scale
development. Psychological assessment. 1995;7(3):309-19.
5.
Novik TS. Validity of the Child Behaviour Checklist in a Norwegian sample. European
child & adolescent psychiatry. 1999 Dec;8(4):247-54. PubMed PMID: 10654117. Epub
2000/02/02. eng.
6.
Novik TS. Child Behavior Checklist item scores in Norwegian children. European
child & adolescent psychiatry. 2000 Mar;9(1):54-60. PubMed PMID: 10795856. Epub
2000/05/05. eng.
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