Title:
Maternal smoking as a risk factor for childhood intussusception
Subtitle title:
Maternal smoking and intussusception
Authors:
Yasuo Nakahara *Correspondence
Department of Pediatric Surgery, Okayama Medical Center, National
Hospital Organization, 1711-1 Tamasu, Kita-ku, Okayama 701-1192,
Japan
Phone: +81-86-294-9911, Fax: +81-86-294-9255
e-mail: ynakahara@okayamamc.jp
Takashi Yorifuji
Department of Human Ecology, Okayama University Graduate School ofEnvironmental and Life Science, 3-1-1 Tsushima-naka, Kita-ku, Okayama
700-8530, Japane-mail: yorichan@md.okayama-u.ac.jp
Toshihide Kubo
Department of Pediatrics, Okayama Medical Center, National Hospital
Organization, 1711-1 Tamasu, Kita-ku, Okayama 701-1192, Japane-mail: kubocchi@okayamamc.jp
Hiroyuki Doi
Department of Epidemiology, Okayama University Graduate School of
medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho,
Kita-ku, Okayama 700-8558, Japane-mail: h-doi@md.okayama-u.ac.jp
Acknowledgements:
This study is partly supported by Grant for Strategies for Efficient Operation1

of the University (2007030201). The authors thank Saori Irie for her help in
preparing the manuscript.
Ethics:This study was approved by the Institutional Review Board at Okayama
University Graduate School of Medicine, Dentistry, and Pharmaceutical
Sciences (no.1506-073).
Conflicts of interests:
The authors have no conflicts of interest to disclose.

2

Title:Maternal smoking as a risk factor for childhood intussusception

Running title:
Maternal smoking and intussusception

Abstract:
Risk factors for intussusception have only rarely been reported. We examined
the association between the risk of hospital admission for intussusception and maternalsmoking, using nationwide population-based longitudinal survey begun in Japan in
2010. Maternal smoking status was queried at 6 months of age, and responses toquestions at 18 months of age about history of hospitalization for intussusception during
the previous year were used as an outcome of interest. We conducted logistic regression
analyses controlling for potential confounding factors. Maternal smoking increased therisk of hospitalization for intussusception (adjusted OR = 2.75, 95% CI 1.09–6.96)
compared with not smoking and a dose-response relationship was observed for the
association. Maternal smoking is associated with an increased risk of intussusception
development in children between the ages of 6 and 18 months.

Key Words:
Children; Epidemiology; Intussusception; Maternal smoking

Abbreviations:CI

Confidence interval

MHLW

Ministry of Health, Labor, and WelfareOR

Odds ratio

Contents:
131 words for abstract,1988 words for manuscript,
3

4 tables, and 1 figure

4Introduction
Intussusception is the most common cause of intestinal obstruction among
infants and young children. The condition develops when a proximal segment ofintestine invaginates into a distal segment of intestine, resulting in intestinal
5

obstruction and constriction of the mesentery. The pathogenesis of idiopathic
intussusception is not well established, but it has been hypothesized that altered bowel
motility or a mass like enlarged Peyer’s patch acting as a lead point induces animbalance in the longitudinal forces of the intestinal wall and causes intussusception.
Reduction is generally accomplished by ultrasonography or fluoroscopically guided10

enema. If reduction by enema fails, surgical reduction is required. Untreatedintussusception eventually leads to bowel necrosis and is potentially fatal. According to
one epidemiological study in Japan, annual incidence of intussusception is 170–180
cases per 100,000 children1.
Despite being a common abdominal emergency disease, risk factors for

15

intussusception have rarely been documented. One well-recognized risk factor is viraland bacterial gastroenteritis2-4, which may alter bowel motility, causes swelling of thelymphoid tissue of the intestine and lead to an increased risk of intussusception.
Considering the possible mechanism of intussusception, identifying other factors that
may alter bowel motility is important. Although maternal smoking is reported to20

increase the risk of gastrointestinal dysregulation in infants (i.e., altering bowel
5motility)5-7, no study to date has evaluated the risk of intussusception in relation tomaternal smoking.
We used a nationwide survey to evaluate the effect of maternal smoking on
the risk of hospital admission for intussusception between the ages of 6 and 18 months.
5

Methods
Participants
The Japanese Ministry of Health, Labor, and Welfare (MHLW) has conducted anannual survey on newborn infants and their parents since 2010. The purpose of this10

survey, known as the Longitudinal Survey of Newborns in the 21st Century is to help
the MHLW develop strategies in response to the rapidly declining Japanese fertility
rate. Questionnaires were sent to all families in Japan with a baby (or babies) born
between the 10th and 24th of May 2010, when the newborns were 6 months old.
Among the 43,767 questionnaires mailed, 38,554 were completed and returned (a15response rate of 88.1%). Follow-up questionnaires have been sent to these participants
every year (at age 18, 30, and 42 months, and so on). Data from 2010 to 2012 (i.e., 1st
to 3rd survey) are currently available from the MHLW. Birth records from Japanesevital statistics are also linked to each child in this survey. Birth record data include
birth length, birth weight, gestational age, singleton or multiple birth, sex, and parental

20

age. Although several reports have suggested the possibility of an increased risk of6

intussusception after current rotavirus vaccination (RotaTeq (Merck, Sharp & Dohme,
Kenilworth, NJ) and Rotarix (Glaxo SmithKline, Brentford, Middlesex, UK) )8-10,
participants of this survey were born before the introduction of the new rotavirus
vaccination program in Japan.
5

In the present study, we used data from the first (i.e., 6 months) and second
surveys (i.e., 18 months), because maternal smoking status was queried only at the firstsurvey and incidence of intussusception is considered to be high during the period (i.e.,
6 and 18 months)11. Children with missing information on maternal smoking status in
the first survey (n = 110) and those with missing information on hospitalization due to10

intussusception (n = 6,484) were excluded, leaving a total of 31,960 participants for the
analysis (Figure 1).

Maternal smoking
Maternal smoking status data were collected at the first survey. Based on responses to15

whether a mother smoked, maternal smoking status was used to divide participants into
non-smokers and smokers. Smoker status was further categorized into two levels basedon responses about the number of cigarettes smoked per day: light smokers (≤ 10
cigarettes/d) and heavy smokers (> 10 cigarettes/d).

20

Hospital admission for intussusception7

Hospital admission for intussusception was queried at the second survey. Responses toa question about history of hospitalization owing to intussusception during the past
year (i.e., between the ages of 6 and 18 months) were used as outcomes of interest.

5

Statistical Analysis
To evaluate the impact of excluded children, we first compared baseline characteristics
between eligible children, children who were included in the analysis, and those who
were excluded from the study. We then carried out a univariate analysis to investigate
associations between children who had been hospitalized owing to intussusception

10(intussusception cases) and baseline characteristics of children and parents.
To evaluate the relationship between maternal smoking (non-smoker vs.
smoker) and hospital admission for intussusception, we conducted logistic regression
analysis. We first estimated crude ORs with CIs for the hospital admission, using
non-smokers as a reference. We then adjusted for sex and maternal age at delivery.

15

Finally, we adjusted for child and parental factors. Child factors included sex(dichotomous), singleton birth or not (dichotomous), term or preterm birth (< 37 weeks
of gestation age) (dichotomous), infant feeding status (exclusively formula fed,
partially breast fed, and exclusively breast fed; categorical) and parity (0 and > 1 birth;
dichotomous). Family factors included maternal age at delivery (< 25, 25–29, 30–34, ≥20

35 years old; categorical), and paternal smoking status (dichotomous).
8Sex of the child, singleton birth or not, term or preterm birth, parity, andmaternal age at delivery were listed in the birth record. Infant feeding practice andpaternal smoking status were ascertained at the first survey (i.e., 6 months of age).
The same analysis was repeated to determine dose–response relationships
5

between maternal smoking and the risk of intussusception by further categorizing thesmoker status into three levels. We used the following categories for maternal smoking
status: non-smoker, light smoker, and heavy smoker. Again, we used the category of
non-smoker as a reference.
All CIs were calculated at 95% and P values < 0.05 were considered10

statistically significant. STATA statistical software (STATA SE version 13, STATA
Corp., College Station, TX) was used for all the analyses.
This study was approved by the Institutional Review Board at Okayama
University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences(no.1506-073).

15

Results
Characteristics of the Study Population
Table 1 shows the baseline characteristics of eligible children, those who were includedin the analyses, and those who were excluded. Compared with the included children,
20

those who were excluded from the study were more likely to be preterm births,
9

formula fed, and to have young mothers and parents who smoked.

Univariate Analysis of Factors Associated with Hospitalization
The risks of hospitalization for intussusception according to the demographic
5characteristics of children and parents are shown in Table 2. A total of 50
intussusception cases were reported with an incidence of 166 cases/100,000 children/y.
Despite a slight predominance among boys, and in the categories of term birth, parity >1, partially or exclusively breast fed, and maternal age at delivery of 30–34 year, noneof the characteristics increased the risk statistically significantly.

10

Multivariate Analysis of Factors Associated with Intussusception
Table 3 shows crude and adjusted ORs with 95% CIs for the risk of intussusception in
relation to maternal smoking. Maternal smoking was associated with increased risk of
hospitalization owing to intussusception in the fully adjusted model (adjusted OR =15

2.75, 95% CI 1.09–6.96).
When we further categorized the smoker status into three levels, we observeda dose–response relationship between maternal smoking status and the risk ofintussusception (Table 4). The risk became strongest when mothers smoked heavily(i.e., more than 10 cigarettes/d) and the adjusted ORs were 1.76 (95% CI 0.52–5.98)

20

for light smokers and 6.82 (95% CI 1.98–23.52) for heavy smokers compared with10

non-smokers.

Discussion
We examined the association between maternal smoking and the risk of hospital
5

admission for intussusception among young children in a nationally representative
sample in Japan. We found that maternal smoking increased the risk of hospital
admission for intussusception between the ages of 6 and 18 months. We also observeda dose–response relationship between maternal smoking status and the risk ofintussusception. To the best of our knowledge, this is the first population-based study10

to examine the association between maternal smoking and the development of
intussusception.
Several risk factors for intussusception have previously been examined. Bothviral and bacterial gastroenteritis were reported as important risk factors for thedevelopment of intussusception 2-4. Current rotavirus vaccines were also identified as a15

possible risk factor for intussusception, but the magnitude of the association varied
between countries8-10. Although potential confounding-by-indication could not be ruled
out, antibiotic use in childhood was shown to increase the risk of intussusception12.
Exclusive breast-feeding, which stimulates bowel peristalsis to a greater extent thanformula feeding, was reported to be a risk factor for intussusception in a case-control

20

study13. All of these risk factors have an effect on bowel motility, supporting the11hypothesis that altered bowel motility may be part of a possible mechanism, explaining
the associations between these risk factors and the development of intussusception.
The observed association between maternal smoking and intussusception
would be biologically plausible because smoking affects bowel motility. Shenassa et al.
5reported that maternal smoking could be linked to infantile colic throughgastrointestinal dysregulation (i.e., altered bowel motility)5. The physiologicalexplanation of this association is that smoking increases plasma and intestinal motilinlevels14, and high levels of motilin cause gastrointestinal dysregulation. Motilin is a gut
hormone that is produced in the duodenal and jejunal mucosa and is associated with10

gastrointestinal peristalsis15. Other studies also showed that infants with colic had
higher serum motilin levels than those without colic independent of feeding type16.
Another possible explanation is that maternal smoking increases the risk ofgastroenteritis, which leads to the development of intussusception. Indeed, Newman etal. demonstrated that maternal smoking was associated with gastroenteritis

15

hospitalization (OR1.2, 95% CI 1.1–1.4)17. Other studies have also noted thatenvironmental tobacco smoke exposure could lead to acute gastroenteritis, especiallyin young children 18,19.
The strength of our study is its large nationally representative sample andprospective cohort design, which supports the generalizability of our findings.

20

Approximately 5% of all infants born within a 1-year period in Japan were included in
12this survey. The large sample size allowed us to examine the effect of maternalsmoking on a disease with a rare incidence (i.e., intussusception), even in the analysis
that aimed to elucidate the dose–response relationship between maternal smoking andthe hospitalization for intussusception.
5

There are some limitations to this study. First, the information for maternalsmoking status and hospitalization for intussusception were based on self-reporting byfamily members, which has the potential for misclassification. However, themisclassification would be non-differential, moving the effect estimates toward thenull20. Second, a lack of an objective tool to determine maternal tobacco smoking

10

status, such as cotinine measurement, or a lack of information on change in maternalsmoking behavior during the study period would cause another potential
misclassification bias, which may also move the effect estimates toward the null. Third,
loss to follow-up may be a concern. Because a loss was more common among thegroup with possible high-risk factors for intussusception, such as children with15

smoking mothers, we may have underestimated the positive association between
maternal smoking and the development of intussusception. Fourth, we only included
the hospitalization for intussusception between 6 and 18 months of age, which may
limit generalizability of the finding. However, approximately 58.0% of theintussusception cases in Japan were reported to occur under the age of 1 y 11 and the20

incidence of 166 cases/100,000 children per year in this study was very close to the13annual incidence of intussusception in Japan reported previously (170–180 cases per
100,000 children)1. Thus, most of the hospitalizations for intussusception wereconsidered to occur during the period we examined in our study.
In conclusion, this is the first population-based study to show an association
5

between maternal smoking and the development of intussusception. Although further
studies are warranted to confirm this finding, maternal smoking cessation may reduceincidence of intussusception. The result has a significant implication for theimportance of smoking cessation, especially among childbearing women.

10

15

20
14

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2. Nylund CM, Denson LA, Noel JM. Bacterial Enteritis as a Risk factor forChildhood Intussusception: A Retrospective Cohort Study. J Pediatr, 2010;
156(4):761-765
3. Mansour AM, El Koutby M, El Barbary MM, et al. Enteric viral infections as
potential risk factors for intussusception. J Infect Dev Ctries, 2013; 7(1):28-35

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4. Muhsen K, Kassem E, Efraim S, Goren S, Cohen D, Ephros M. Incidence and risk
factors for intussusception among children in northern Israel from 1992 to 2009: a
retrospective study. BMC Pediatrics, 2014; 14:218
5. Shenassa ED, Brown MJ. Maternal Smoking and Infantile Gastrointestinal
Dysregulation: The Case of Colic. Pediatrics, 2004; 114(4):e497-e505.

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6. Reijneveld SA, Brugman E, Hirasing RA. Infantile colic: maternal smoking as
potential risk factor. Arch Dis Child, 2000; 83:302-303.
7. Sondergaard CH, Henriksen TB, Obel C, Wisborg K. Smoking during pregnancy
and infantile colic. Pediatrics, 2001; 108(2):342-346.
8. Haber P, Patel M, Pan Y, et al. Intussusception After Rotavirus Vaccines Reported20

to US VAERS, 2006-2012. Pediatrics, 2013;15

131(6):1042-1049.

9. Yih WK, Lieu TA, Kulldorff M, et al. Intussusception risk after rotavirus
vaccination in U.S. infants. N Eng J Med, 2014 370: 503-512
10. Weintraub ES, Baggs J, Duffy J, et al. Risk of Intussusception after Monovalent
Rotavirus Vaccination. N Eng J Med, 2014; 370:513-519.
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Ito Y, Kusakawa I, Ukiyama E, et al. Japanese guidelines for the management of
intusussception in children, 2011. Pediatr Int, 2012; 54(6): 948-958

12. Hviid A, Svanström H. Antibiotic use and intussusception in early childhood. J
Antimicrob chemother, 2009; 64(3):642-648.
13. Pisacane A, Caracciolo G, Luca UD, et al. Infant feeding and idiopathic
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intussusception. J Pediatr, 1993; 123(4):593-595.
14. Bell JS, DiMagno EP, GoVLW. Cigarette smoking alters the human interdigestive
migrating moter complex. Clin Res, 1981; 39:303A.
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Lothe L, Ivarsson SA, Lindberg T. Motilin, Vasoactive intestinal peptide andgastrin in infantile colic. Acta Pediatr Scand, 1987; 76(2):316-320.

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Lothe L, Ivarson SA, Ekman R, Lindberg T. Motilin and infantile colic. A
prospective study. Acta Paediatr Scand, 1990; 79(4):410-416.

17. Newman RD, Grupp-Phelan J, Shay DK, Davis RL. Perinatal risk factors for
infant hospitalization with viral gastroenteritis. Pediatrics, 1999; 103(1):e10318. Özmert EM, Kiliç M, Yurdakö K, et al. Environmental tobacco smoke: Is it a risk
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factor for diarrhea in 6-18 months old infants? Cent Eur J Public Health, 2008;16

16(2): 85-86.
19. Kum-Nji P, Mangrem CL, Wells PJ, Herrod HG. Is environmental tobacco smoke
exposure a risk factor for acute gastroenteritis in young children? Clin Pediatr(Phila), 2009; 48(7): 756-762.
5

20. Rothman KJ. Epidemiology: An Introduction.2nd ed. Oxford; New York: Oxford
University Press; 2012.

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15

20
17

Table 1. Demographic characteristics of eligible children (n=38444)
Total(eligible)(N=38444)

Included

Excluded(N=31960)(N=6484)

19796 (51.5)
18648 (48.5)

16504 (51.6)
15456 (48.4)

3292 (50.8)
3192 (49.2)

0.2037721 (98.1)
723 (1.9)

31378 (98.2)
582 (1.8)6343 (97.8)
141 (2.2)

0.0636353 (94.6)
2091 (5.4)

30276 (94.7)
1684 (5.3)

6077 (93.7)
407 (6.3)<0.01

18030 (46.9)
20414 (53.1)

14965 (46.8)
16995 (53.2)

3065 (47.3)
3419 (52.7)

0.511337 (3.5)
23928 (62.2)
12853 (33.4)
326 (0.9)1007 (3.2)
19786 (61.9)
10937 (34.2)
230 (0.7)330 (5.1)
4142 (63.9)
1916 (29.6)
96 (1.5)

<0.01

<30

14614 (38.0)

11365 (35.6)

30-34

14189
(36.9)

12231 (38.3)

35≦9641 (25.1)

8364 (26.2)

35757 (93.0)
2687 (7.0)

30170 (94.4)
1790 (5.6)

p-valuesc

Characteristics of children
Sex, n (%)a
Boys
Girls
Singleton or Multiplea
Singleton birth, n (%)
Multiple birth, n (%)
Maturity at birtha
Term birth, n (%)
Preterm birth, n (%)
Parity, n (%)a0
≥ 1Breast Feeding Status,n(%)bExclusively formula fed
Partially breast fed
Exclusively breast fed
Unknown
Parental characteristics
Maternal age at delivery, n(%)aMaternal smoking status, n(%)bNon-smoker
SmokerPaternal smoking status, n

18

3249
(50.1)
1958(30.2)
1277(19.7)

5587 (86.2)
897 (13.8)

<0.01

<0.01

(%)b
Non-smoker
SmokerUnknown

21945 (57.1)
15623 (40.6)
876 (2.3)

18884 (59.1)
12483 (39.1)
593(1.9)3061 (47.2)
3140 (48.4)
283 (4.4)<0.01

a Obtained from the birth recordb Obtained from the first survey (at the age of 6 months)c P-values from chi-square tests to compare differences between included children andexcluded children
Table 2. Univariate analysis of Sociodemographic Factors Associated with Intussusception(n=31960)

Characteristics of children
Sex, n (%)
Boys (n=16504)
Girls (n=15456)
Singleton or Multiple, n (%)
Singleton birth (n=31378)
Multiple birth (n=582)
Maturity at birth, n (%)
Term birth (n=30276)
Preterm birth (n=1684)
Parity, n (%)
0 (n=14965)≥ 1 (n=16995)

Intussusception
cases
n=50

No intussusception
cases
n=3191029 (0.18)
21 (0.14)

16475 (99.8)
15435 (99.9)

0.37

49 (0.16)
1 (0.17)31329 (99.8)
581 (99.8)

0.93

48 (0.16)
2 (0.12)30228 (99.8)
1682 (99.9)

0.69

20 (0.13)30 (0.18)

14945 (99.9)
16965 (99.8)

0.33

1 (0.10)1006 (99.9)

0.81

33 (0.17)

19753 (99.8)

16 (0.15)

10921 (99.9)

12 (0.11)

11353 (99.9)

27 (0.22)

12204 (99.8)

p-valuesa

Breast Feeding Status, n (%)
Exclusively formula fed(n=1007)
Partially breast fed (n=19786)
Exclusively breast fed(n=10937)
Parental characteristics
Maternal age at delivery, n (%)<30 (n=11365)
30-34 (n=12231)

19

0.07

35≦ (n=8364)
Paternal smoking status, n (%)
Non-smoker (n=18884)
Smoker (n=12483)

11 (0.13)

8353 (99.9)

29 (0.15)
20 (0.16)

18855 (99.9)
12463 (99.8)

a P-values from chi-square tests

20

0.88

Table 3. Crude and adjusted ORs (with their 95% CI) for the associations of maternal smoking with intussusception.
Total
numberIntussusception
cases
n (%)

crude OR

Adjusted ORa

Adjusted ORb

30170
1790

44 (0.15)
6 (0.34)

1 (ref)2.30 (0.98-5.41)

1 (ref)
2.51 (1.06-5.91)

1 (ref)2.75 (1.09-6.96)

Maternal smoking
status
Non-smoker
Smokera Adjusted for sex and maternal age at deliveryb Adjusted for child factors (sex, singleton or not, term or not, breast feeding status, and parity) as well as parental

factors (maternal age at delivery and paternal smoking status).

21

Table 4. Crude and adjusted ORs (with their 95% CI) for the associations of amount of maternal smoking with intussusception.
Total

Intussusception
cases
n (%)

crude OR

Adjusted ORa

Adjusted ORb

30170
1383

44 (0.15)
3 (0.22)1 (ref)
1.49 (0.46-4.80)

386

3 (0.78)

5.36 (1.66-17.35)

1 (ref)
1.63 (0.51-5.29)
5.62(1.74-18.20)

1 (ref)
1.76 (0.52-5.98)
6.82(1.98-23.52)

Maternal smoking status
Non-smoker
light smoker (0-10/day) cheavy smoker (>10/day) ca Adjusted for sex and maternal age at deliveryb Adjusted for child factors (sex, singleton or not, term or not, breast feeding status, and parity) as well as parental factors(maternal age at delivery and paternal smoking status).
c A total of 21 participants are excluded (from Table 3) owing to missing information on number of cigarettes smoked per day.

22

Figure caption
Figure 1. Flow diagram of the selected participants.

23