Pacifier use as a risk factor for reduction in breastfeeding duration : a systematic review

This systematic review of literature proposes to establish whether pacifier use is a risk factor for a reduction in the duration of breastfeeding. A search of the Medline and Lilacs databases was carried out for articles published between 1996 and 2006 using the following descriptors: “breastfeeding” and “pacifier”. Articles were excluded if they: had no open access abstracts; did not contain estimators testing the degree of association between breastfeeding duration and pacifier use; involved a follow-up loss of greater than 20%; were written in languages other than Portuguese, English and Spanish; covered specific population categories, such as pre-term babies or mothers who experienced difficulty breastfeeding; or were based on information provided by the mother or a health care professional. Nineteen articles were chosen according to the criteria outlined above; of these, one was a randomized clinical trial, eleven were prospective cohort studies and seven were cross sectional studies. The review concludes that pacifier use is a risk factor for breastfeeding duration, although the performance mechanism remains obscure. Other risk factors relate to the children, their parents and the hospital care they receive regarding the early interruption of breastfeeding. There is a need to standardize the methodology for investigating the association between pacifier use and breastfeeding duration, in order to provide scientific knowledge on this subject.


t h a t p a c i f i e r u s e i s a r i s k f a c t o r f o r b re a s t f e e d i n g d u r a t i o n , a l t h o u g h t h e p e r f o r m a n c e m e c h a n i s m remains obscure. Other risk factors relate to the children, their parents and the hospital care they receive re g a rd i n g t h e e a r l y i n t e r r u p t i o n o f b re a s t f e e d i n g . T h e re i s a n e e d t o s t a n d a rd i z e t h e m e t h o d o l o g y f o r
investigating the association between pacifier use and breastfeeding duration, in order to provide scientific knowledge on this subject.have a detrimental effect on the duration of breastfeeding.

Palavras-chave
In view of the facts described above, this systematic review of the literature aims to establish how the relation between pacifier use and breastfeeding duration is presented in the scientific literature on the subject.

Methods
Articles addressing the association between breast-  The randomized clinical trial of Centuori et al. 21uld not be used because it was testing a medication that aimed to prevent breast diseases, which are considered limiting factors for breastfeeding duration.
The study of Barros et al. 22 was excluded for testing an association between birth weight and pacifier use as well as birth weight and breastfeeding duration and therefore not testing the variables of interest for this review; the study carried out by Kramer et al.. 8 was also excluded because it tested the effects of counseling mothers on breastfeeding, thereby discouraging the use of a pacifier and not testing it as a predictor of breastfeeding duration.
The study of Collins et al. 23 used a sample of pre-term babies; Cunha et al. 24 were also excluded The study performed by Görbe et al. 13 32 Vieira et al. 33 and Vieira et al. 34 did not control for confounding factors.
The confounding factors that remained statistically significant (p<0.05) after a multivariate analysis are also presented in Table 3.This shows that these factors are also associated to the duration of breastfeeding.Although they attenuate the effects of pacifier use over duration of breastfeeding, the effect is not completely canceled out.To facilitate visualization, the studies were distributed according to variable type, in so far as it relates to the child, the mother, the father or the place of birth.
6][37][38][39][40] In addition, the level of education of the mother 27,29,31,37,41 and the age of the mother, 29,31,36,39,[41][42][43] as well as smoking during pregnancy 29,31,42,43 and returning to work [42][43][44] had a significant impact on the duration of breastfeeding.The level of education of the father seems to be important for the duration of breastfeeding owing to the fact that a father 's support for breastfeeding practices apparently extends its duration. 29,43,45e variables relating to hospital care appear to be critical, since hospitals encourage breastfeeding, but most of the selected articles did not control these variables making it impossible to determine whether hospital care influences the duration of breastfeeding or not.
be excluded, since it did not perform a direct association between exclusive breastfeeding duration and pacifier use or breastfeeding and pacifier use.
Likewise the article by Kelmanson 28 was excluded because it did not establish a relation between breastfeeding duration and pacifier use, even though it shows a statistically significant relation between a pattern of exclusive breastfeeding, formula feeding and bottle feeding with pacifier use.

Results
Nineteen articles were finally chosen to be included: one randomized and controlled clinical trial, nine cohort studies and eight cross-sectional studies.
Table 1 presents brief descriptions of the selected articles.
Most of the studies had no follow-up loss and claim that they had to make exclusions along the way to get to their final sample.These exclusions were not due to follow-up loss but resulted from the inclusion and exclusion criteria of each study.
The minimum follow-up duration was three Telephone interviews were used by most of the cohort studies, even though personal contact at the hospital and home visits had an important impact on the quality of information.Recall diaries were also used to confirm information and train researchers and or health professionals.The structured interviews provide evidence of the authors' commitment to ensuring good quality data collection.Table 2 presents the studies according to patterns of breastfeeding.
Sixteen articles found a direct association between breastfeeding duration and pacifier use, ten found a direct association between exclusive breastfeeding and pacifier use, and three articles considered full breast feeding and pacifier use.It was observed that the variables of interest did not establish a pattern for the answers, which could be either qualitative binomial or ordinal qualitative, or even nominal in the case of several categories.
Pacifier as risk factor for breastfeeding duration

Table 2 conclusion
Breastfeeding duration versus pacifier use.
# Univariate analysis was performed using χ 2 .oddsratio and relative risk using the information' described in the tables.

Santos Neto ET et al.
ones obtained form cohort studies.The other authors of cross-sectional studies extrapolate their analysis methods using univariate and multivariate analysis, multiple logistic regressions and estimating risk using prevalence and odds ratios. 29,46e present review establishes clearly the role of pacifier use as a determining factor for duration of breastfeeding, since the selected studies, regardless of design, show extremely significant levels of association even when controlled for confounding factors.6][37][38][39][40] It is believable that the introduction of other foods influences the child to ask less often for the mother 's breast, also to reach satiation quicker and to abandon breastfeeding early, even when being fed with an inadequate diet.However, the explanation, whether physiological or behavioral, for the reduction of breastfeeding duration through use of a pacifier remains inconclusive.In an attempt to explain this, three hypotheses can be suggested.
The first claims that the pacifier does not have a direct biological effect on the child; instead, it would be a marker of difficulty, inability or insecurity on the part of the mother with regard to breastfeeding. 25,35The second hypothesis focuses on the pacifier acting as a method for suppressing crying and concealing difficulties experienced by the mother.This hypothesis argues that, in reality, a nipple confusion takes place.This may be due to mechanical differences and different sucking patterns established by the child for the mother 's nipple and the teat of the bottle. 47This phenomenon would lead the child to opt for sucking artificial nipples instead of the mother's.
The third, solely based on breastfeeding physiology, advocates the hypothesis that constant use of artificial nipples would diminish the previously intense stimulation of mother 's nipple, consequently reducing the prolactin reflex and milk production.

Discussion
The results indicate that the use of a pacifier has been considered a risk factor for reduction of breastfeeding duration.Only Howard et al. 35  Clinical trials regarding this issue are hard to conduct, since they will always deal with mothers and babies.However, we were able to find articles that dealt with mothers who had trouble breastfeeding and high risk babies because, when dealing with these groups, studies are more easily permitted, since they follow a principle of benefit to health of sample individuals.These studies could not be included in the analysis due to exclusion criteria adopted.
Therefore the cohort studies were the most common type used to evaluate factors interfering in breastfeeding duration.Periodical data collection allows a longitudinal analysis capable of measuring risk factors that reduce or increase breastfeeding duration.Only Santiago et al,. 30Nelson et al., 31 Vogel et al. 41 and Mascarenhas et al. 43

Conclusions
The use of a pacifier was unanimously defined as a risk factor for the reduction of breastfeeding duration, exclusive or not.However, the mechanisms by which pacifiers act on the reduction of breastfeeding duration still remain obscure.
Several factors, relating to the mother, the child, the father and hospital care, interfere with the duration of breastfeeding, with the result that this is a complex phenomenon that should be studied in all its dimensions.
Future studies assessing length of breastfeeding should follow a standardization of any methodological elements to allow for the synthesizing of scientific knowledge of this phenomenon. duration.
This study considers it a slight possibility that it was not possible to find articles that present a nonsignificant association between pacifier use and breastfeeding duration, because references cited in the articles under review were also analyzed, with a view to making the review more thorough and avoiding bias selection.After exhaustive research, only Audi et al. 46 mentioned that Perez-Escamilla et al. 48found a non-significant association between pacifier use and breastfeeding duration.However, more in-depth analysis revealed that Perez-Escamilla et al. 48 Breastfeeding, Pacifiers, Weaning Resumo Esta revisão sistemática da literatura se propõe verificar se o uso de chupeta é um fator de risco para re d u ç ã o d o t e m p o d e a m a m e n t a ç ã o .F o r a m pesquisadas as bases de dados Medline e Lilacs, no p e r í o d o d e 1 9 9 6 a 2 0 0 6 , u t i l i z a n d o o s t e r m o s : " a l e i t a m e n t o m a t e r n o " e " c h u p e t a " , " a m a m e nt a ç ã o " .F o r a m e x c l u í d o s a r t i g o s : s e m re s u m o ; s e m descrição ou referência a estimadores de associação entre tempo de amamentação e uso de chupetas; com o índice de perda amostral superior a 20%; escritos em outros idiomas diferentes do português, inglês e e s p a n h o l ; c o m a b o rd a g e m à p o p u l a ç ã o d e b e b ê s prematuros ou à mães com dificuldades de amamentação; e, com informações relatadas por outros indiv í d u o s d i f e re n t e s d a m ã e o u p ro f i s s i o n a l d e s a ú d e .F o r a m s e l e c i o n a d o s 1 9 a r t i g o s : u m e n s a i o c l í n i c o randomizado controlado, 11 estudos de coorte e sete estudos transversais.Conclui-se que uso de chupeta é u m f a t o r d e r i s c o p a r a a re d u ç ã o d o t e m p o d e amamentação, entretanto permanece obscuro qual o s e u m e c a n i s m o d e a t u a ç ã o .O u t ro s f a t o re s d e r i s c o re l a c i o n a d o s à c r i a n ç a , à m ã e , a o p a i e a o a t e n d imento hospitalar também influenciam nesse processo.É n e c e s s á r i o a p a d ro n i z a ç ã o d e e l e m e n t o s metodológicos que investiguem a associação entre o uso de chupetas e a duração da amamentação visando sintetizar o conhecimento científico.
for including children whose birth weight was under three kilos and healthy, which suggested that the greater part of this sample consisted of pre-term babies, thereby restricting the possibility of interpreting the results.Dewey et al.'s25 study could not be included in the analysis either, because it did not make a direct association between pacifier use and breastfeeding duration, despite associating the early use of pacifier by mothers who received health care for one week only.Even though Hornell et al.'s26 study conducted a partial analysis of the data set also used by Aarts et al.,27 which was included in the evaluation, it had to excluded because there was a between 1996 and 2006.Thirty-one were excluded, either because they did not cite estimators, focused on oral health, sudden death syndrome, women's health or pain, or because they were already review articles, were written in German, or did not have an abstract.The second search performed on Medline, this time using the keywords in English, yielded 84 articles.Forty-two of these did not provide references of association between the variables of interest; two did not have abstracts; four were written in other languages such as German, Polish and Danish.After all the exclusions, this second Medline search yielded 36 articles, which were added to the seven found on Lilacs and the ten yielded by the first Mediline.A total of 46 articles were therefore selected to be read in full.Analysis of these 46 articles led to the exclusion of a further 18, because they appeared on more than one database.The study finally included therefore a total of 26 articles.Most of the selected articles are available online at CAPES Portal, when accessing through a federal institution.The authors of articles unavailable online were contacted by e-mails asking for the articles of interest.The Network of Federal Libraries in Brazil was used to recover articles.Thirty-three complete articles were read.These were classified as follows: five randomized and controlled clinical trials, two case-control studies, 18 cohort studies, and eight cross-sectional studies.To be included in the analysis the articles had to perform a direct association between exclusive breastfeeding duration and pacifier use or breastfeeding and pacifier use; the information regarding this must have been provided by the mother or a health care professional; the follow up loss could not be greater than 20%; the studies could not focus on specific population categories such as pre-term babies or mothers who had trouble with breastfeeding, because these kinds of groups usually get treated differently and this can interfere as a confounding factor in the study.These criteria were based on Ullah & Griffiths 12 systematic review.
months and the maximum was 12 months.As for the cross sectional studies, they grouped together children aged from four months until two years of age.The largest sample size was found in Mikiel-Kostyra et al., 29 who studied 11,422 mother-infant pairs, while Santiago et al. 30 used the smallest-only 101.
did not perform a survival analysis, describing only multivariate analysis with multiple logistic regressions.Despite presenting the same risk relation between pacifier use and duration of breastfeeding, these studies could have used their information better and compared it with other studies, has they carried out a survival analysis.Cross-sectional studies are important because they can involve large samples and a large amount of data, which is practically impossible when dealing with clinical trials and cohort studies, owing to their high cost.Nevertheless, cross-sectional studies are recommended for diagnosis of the situation at the present time, but are not suitable for future predictions or risk estimates for populations.When dealing with pacifier use and its association with duration of breastfeeding it is possible to measure percentiles of use and defined lengths of breastfeeding based on recall information collected from the mother.This is only possible because weaning is considered a key moment in the mother's life and they always remember the month when it happened.Silveira and Lamounier 45 and Minagawa et al. 40 in survival analyses of cross-sectional data, establish risk estimates significantly similar to the Pacifier as risk factor for breastfeeding duration 24 months.Regarding variables of interest, pacifier use up to the first 30 days should be dichotomized, while the others should be collected in a simplified way, always dichotomized when qualitative and always numerical when quantitative, avoiding use of intervals that can complicate the comparability of results.The Survival Analysis with Cox Regression using an adjusted Hazards Ratio as an estimator should be the method chosen for statistical analysis, always presenting significance values, risk calculations and their respective confidence intervals.

2008 378 Santos Neto ET et al.
ding duration have been in the spotlight ever since Victora et al. 2 first published an article in an international journal associating breastfeeding duration with the use of a pacifier.This article examines studies of the repercussions of pacifier use on child health.Rev.Bras.Saúde Matern.Infant., Recife, 8 (4): 377-389, out./ dez., 31 Aarts et al.27and Nelson et al.31chi- was excluded because it did not show an adequate association between breastfeeding at the sixth month and pacifier use but merely described that, in a group of 136 non-pacifier users, eight stopped breastfeeding before the sixth month.Rev.Bras.Saúde Matern.Infant., Recife, 8 (4): 377-389, out./ dez., 2008 Santos Neto ET et al.

Table 1
Categorization of studies according to study desingn.
continue Santos Neto ET et al.*Both studies used a sub-sample to check the association between pacifier use and breastfeeding duration.

Table 2
Breastfeeding duration versus pacifier use.
did not investigate the relation between pacifier use and breastfeeding duration, but rather the influence of a cloth or rag soaked or boiled in herbal infusions placed in the infant's mouth (a method called "chupón", which is commonly used in Honduras) on breastfeeding duration.This systematic review suggests the need for standardization of methods for any further studies to be carried out, to ensure that it is possible to synthesize the results in a meta-analysis.Based on the majority of the studies found, subsequent studies on breastfeeding should be designed as prospective cohorts, calculating sample sizes in advance and following up for six months when assessing exclu- e crianças de primeira infância e também a de produtos de puericultura correlatos.Diário Oficial República Federativa do Brasil, Brasília, DF, 04 jan.2006.[acesso em: 13 dez.2006].Disponível em: <Http://www6.senado.gov.br/sicon/listareferencias.action?codigobase=2&codigodocu-mento=253662>