The Association Between Infant Temperament and Breastfeeding Duration: A Cross-Sectional Study

Abstract

Background:

Little is known about the relationship between infant temperament and breastfeeding. The few studies investigating this report mixed results. Some suggest that difficult infants are breastfed for shorter duration, others report opposing results or no association between the two.

Aim:

This study investigated associations between infant difficult temperament and breastfeeding duration in a nationally representative cohort of Irish 9-month-old infants.

Methods:

Breastfed, normal birth-weight singletons from The Infant Cohort of the Growing Up in Ireland Study (n = 5,955) were considered in this research. The Infant Characteristics Questionnaire (ICQ), completed by the mother, was used to assess four different dimensions of difficult temperament: fussy, unpredictable, unadaptable, and dull. Our main interest was the fussy dimension as this is captured best by the ICQ. Initially, a logistic regression (LR) model having the binary version, short (<90 days) or long breastfeeding (≥90 days) as outcome variable, was constructed. Next, a proportional odds logistic regression (POLR) model examining the five-level categorical version (≤1 week, 2 weeks-<1 month, 1-<3 months, 3-<6 months, and ≥6 months) of breastfeeding duration was developed. All regression models were adjusted for relevant sociodemographic data.

Results:

A total of 3,119 infants were breastfed for less than 90 days, while 2,836 were breastfed for 90 days or longer. The LR and POLR models showed a mild inverse association between infant fussiness/difficultness and breastfeeding duration (LR: OR = 0.98, 95% CI: 0.97–0.99, POLR: OR = 0.98, 95% CI: 0.97–0.99). Higher infant unpredictability is associated with longer breastfeeding duration (LR: OR = 1.04, 95% CI: 1.02–1.07, POLR: OR = 1.04, 95% CI: 1.02–1.06).

Conclusions:

In this cross-sectional study, we found that breastfeeding duration was inversely associated with infant fussiness and positively associated with infant unpredictability.

Introduction

Numerous studies report the positive effects of breastfeeding for infant's physical health, development, and cognition.^1–3 Despite recognized benefits and universal promotion, breastfeeding rates remain low in most western countries.^4–6 While most studies focus on maternal and sociodemographic factors,^6,7 little is known about the role of infant temperament for maintaining breastfeeding.

The mother–infant interaction plays a significant role in infant growth and can modulate maternal and infant behaviors. The relationship between mother and infant starts forming from prenatal times; it develops as a dyadic process and it is coregulatory and bidirectional.⁸ With time, this relationship becomes an expression of maternal psychology, infant temperament, and the way this is perceived by the mother.⁹ Previous studies showed that both maternal psychological characteristics and infant attributes (such as irritability, hypo-, or hyperaroused) could influence the goodness-of-fit within the mother–infant dyad and that failure to attain this can lead to the infant being perceived as difficult/demanding with predisposition to long-term negative outcomes.^8,9 In addition, maternal psychological factors such as stress, anxiety, adaptability/flexibility, mother's priorities and mothering self-efficacy, breastfeeding self-efficacy, dispositional optimism, and faith in breast milk can affect breastfeeding duration.^10,11

Infant temperament is an innate and constant characteristic. Temperament has been previously defined as the totality of individual inborn traits, a determinant of the infant's unique behavior and emotional response to external events. Previous studies, including molecular genetics research, have shown that this is constitutional, with a biological basis.^12,13 Of particular relevance to this project, research supports the stability of difficult temperament from the neonatal period through early childhood years,^12–14 and studies examining the convergence between maternal appraisal of infant temperament and home-based observations have demonstrated the validity of maternal report particularly in the case of infant-negative behaviour.^15–17

When investigating breastfeeding and infant temperament, two different approaches have emerged. Most researchers report on the effects of infant temperament on breastfeeding,^18–22 while few investigate the influence of breastfeeding on infant temperament development.^23,24 A recent Norwegian study aimed at assessing the mutual prospective effects between difficult temperament and breastfeeding in a large population reported that difficult infants are less likely to be exclusively breastfed at age 6 months, with no significant associations observed at later ages.²⁵ The same study found no effects of breastfeeding on infant temperament development.²⁵ Other studies also reported negative associations between difficult infant temperament and breastfeeding outcomes.^19–22 It is possible that mothers consider infants that fuss and cry more difficult to breastfeed, using complementary feeding as a soothing element^21,26,27 and this is consistent with reports showing that fussy infants are more likely to be introduced to complementary feeding before the age of four months.²⁸

Several studies have shown that stable breastfeeding patterns are associated with easier to manage, less irritable infant temperament or improved socially responsive behaviors,^18,22,29,30 suggesting a positive association between breastfeeding and infant temperament. However, a recent UK-based study reports that breastfed and mixed-fed (breast milk and formula) 3-month-old babies are more likely to be rated by their mothers as having a more challenging temperament, suggesting possible association between breastfeeding and negative infant temperament.²⁴

In this article, we set out to investigate the association between breastfeeding duration and infant difficult temperament in a large cohort of Irish infants, and we hypothesize that more difficult infants are breastfed for a shorter period.

Methods

Cohort and data collection

This study is using data from the National Longitudinal Study for Children-Growing Up in Ireland (GUI).³¹ The infant cohort-GUI comprises a sample of 11,134 9-month olds, born between December 1, 2007 and June 30, 2008, and their families. The sample was selected on a systematic basis using data from the Child Benefit Register (a current and up-to-date data payment database of all children residing in Ireland).³²

The GUI project received ethical approval from a research ethics committee. Written informed consent was sought from the parents of the infants and data were collected between September 2008 and April 2009.³² The overall response rate was 65%.³²

Trained interviewers administered detailed questionnaires, including a number of relevant standardized instruments to the primary and secondary caregivers in the family home.³¹ These questionnaires were designed to record a wide range of factors associated with the lives of the infants, including health, social, emotional, behavioral background, physical, and mental development.

Measures considered in this study

Breastfeeding duration

At the time of the interview, mothers were asked a series of questions about breastfeeding, including initiation, exclusivity, and duration. The main outcome measure of this study was the breastfeeding duration. This was investigated retrospectively and was initially recorded as the age of the infant in days, weeks, or months when breastfeeding was terminated.³¹ Using these data, we had derived a variable representing the breastfeeding duration in days.

Infant temperament

The Infant Characteristics Questionnaire (ICQ) developed by Bates et al. in 1979 is a standardized screening device and it was used to investigate infant difficult temperament.³³ The 6-month-old version of the questionnaire (ICQ-6) was chosen by the GUI team as this is the most psychometrically developed.³² ICQ-6 contains 24 items rated on a seven-point Likert scale (a value of 1 indicates an optimal temperamental trait, while a value of 7 indicates a more difficult temperament). The instrument generates scores for four different temperamental subscales: fussy (hard to soothe), unpredictable (how easy it is to predict infant's needs), unadaptable (infant's reaction to new events), and dull (infant's social responsiveness and activity level). Reliability tests of the ICQ-6 in the GUI Infant Cohort showed similar results with those found by Bates et al. for all factors with the exception of dull.³² Initial internal consistency coefficients (Cronbach's alpha) measured by Bates et al. (1979) for the fussy, unadaptable, dull, and unpredictable subscales were of 0.79, 0.75, 0.39, and 0.50, while the corresponding coefficients calculated in the GUI pilot study (2008) were of 0.69, 0.71, 0.13, and 0.56, respectively.³²

Correlations between the four temperamental dimensions were quite low, ensuring that none of them was redundant and all four dimensions of the ICQ were included in our analysis. Previous studies support this approach, claiming the additional merit of including temperament in its entirety in the analysis, particularly when difficult behavior is examined.^34–36

As difficult temperament is a constant innate characteristic, we consider that scores for the four temperamental traits recorded at 9 months are representative of infant difficultness from the time of their birth. Our primary interest was the fussy subscale as this was best captured by the ICQ-6 because behavior characterizing this is easier recognized by the mother.³³

Possible confounders

Our covariate selection process was informed by prepublished international literature relevant to breastfeeding.^3,5–7 The infant- and pregnancy-related covariates were birth-weight, infant's sex, and gestational age; maternal factors were age, BMI, health status, marital status, stress, depression, infant's age when the mother returned to work, and smoking habits at the time of the interview. Most variables were directly self-reported by the mother. Maternal BMI was calculated from measures taken at the time of the interview.

Two measures of maternal psychological status, maternal stress and maternal depression, were available in the GUI study and both of these were included as possible confounders. The Parental Stress Scale, assessing both positive and negative aspects of parenthood on four subscales—rewards, stressors, lack of control, and satisfaction, was used to estimate maternal stress.³² A total stress score of between 18 and 90 was calculated for each mother, higher scores indicating higher levels of stress. This scale demonstrated an internal consistency coefficient of 0.83.³² The 8-item short version of the Center for Epidemiological Studies Depression Scale (CESD-8) was used to assess maternal depression.³² This is a widely used self-report instrument measuring depression in the general population. A total depression score ranging from 0 to 24 was assigned to each mother by adding item responses. The CESD-8 correlates highly (r = 0.93) with the full 20-item version scale and showed a high internal consistency coefficient (α = 0.86).³²

The socioeconomic climate of the household was accounted for by household social class, maternal education, and ethnicity. Social class was coded as follows: Professional/Managerial; Other nonmanual/Skilled manual; Semiskilled/Unskilled manual; Never worked-no social designation; in accordance with existent literature using GUI data.^3,6 This classification takes into account the occupation of both caregivers (where applicable), the family social class being assigned on the basis of the higher of the two.

Exclusions

We excluded low birth-weight infants (<2,500 g, N = 406), preterm infants (<35 weeks, N = 117), twins (N = 387), or infants with cleft lip or palate (N = 15). We also excluded dyads where the primary caregiver was not the biological mother of the infant (N = 83), all mothers who suffered of severe illnesses (N = 10) or those who were on medication (N = 12). Finally, we excluded all cases where the information on breastfeeding was incomplete (N = 199). After this, a sample of N = 9,905 infants was available. To investigate associations of infant difficult temperament with breastfeeding duration, we only consider the mother–infant dyads where breastfeeding was initiated (N = 5,955).

Statistical analysis

Breastfeeding duration was the main outcome considered in this study. Two approaches were adopted for statistical analysis. First, we used the median breastfeeding duration (90 days, interquartile range (IQR): 20, 190 days) to divide all breastfed infants into two subgroups: “short” (< 90 days) and “long” breastfeeding (≤90 days). Second, to increase sensitivity of the analysis, a five-level breastfeeding duration variable (1 week or less, 2 weeks to a month, 1–3 months, 3–6 months, and 6 months or longer) was analyzed. This classification is consistent with a previous study investigating the effects of breastfeeding on neurodevelopment in infancy carried out in this cohort.³

First, a logistic regression (LR) model was constructed to examine the role of infant temperament in breastfeeding duration (short vs. long). Next, we developed a Proportional Odds Logistic Regression (POLR) model having the five-level categorical version of breastfeeding duration as outcome variable.

All the covariates considered were initially included in the regression models. We used the Akaike Information Criterion (AIC) as a tool for model selection. Lower AIC scores indicate a better fit of the model. Nonsignificant variables were excluded, except infant temperament dimensions, maternal stress, and depression. The decision to retain these irrespective of their significance was based on relevance to our research question.

Results

Breastfeeding was initiated in 5,955 infants (60%) and 3,950 (40%) infants were bottle-fed from birth. Overall, 3,119 (31%) infants were breastfed for less than 90 days and 2,836 (29%) were breastfed for 90 days or longer. Of all infants breastfed for short duration, 1,019 (33%) were breastfed for less than a week, 808 (26%) for 1 week–month, and 1,292 (41%) were breastfed for 1–3 months. Of all infants breastfed for long duration, 1,229 (43.35%) were breastfed for 3–6 months and 1,607 (56.66%) for more than 6 months. 2,189 (76%) of the mothers who breastfed for 90 days or longer were 30 years of age or older and 1,759 (62%) belonged to a higher social class (Professional/Managerial). The characteristics of the entire cohort are shown in Table 1 (characteristics of nonbreastfed infants are shown for completeness).

Table 1.

Sample Description

			Breastfed for short duration <90 days	Breastfed for long duration ≥90days
	All N = 9905 (100%)	Never-breastfed N = 3950 (39.87%)	N = 3119 (31.48%)	N = 2836 (28.63%)	p-Values^a
Sex of the infant
Male	5046 (51)	2075 (53)	1593 (51)	1378 (49)
Female	4859 (49)	1875 (47)	1526 (49)	1458 (51)	0.06^χ
Birth-weight (g)	3567 (457)	3544 (460)	3572 (447)	3589 (456)	0.16^t
Baby's admission to ICU
Yes	971 (10)	409 (10)	301 (10)	261 (9)	0.58^χ
No	8932 (90)	3540 (90)	2817 (90)	2575 (91)
Mode of delivery
Normal vaginal delivery	6053 (60)	2364 (60)	1819 (58)	1870 (66)
Planned/emergency cesarean	2333 (24)	1031 (26)	735 (24)	567 (20)
Suction/forceps assisted/vaginal breech	1517 (16)	555 (14)	463 (18)	399 (15)	<0.001^χ
Gestational age (weeks)
Late birth (> = 42)	1221 (12)	469 (12)	404 (13)	348 (12)
On time (37–41)	8493 (86)	3394 (86)	2655 (86)	2444 (86)
Somewhat early (35–36)	162 (2)	85 (2)	45 (1)	35 (1)	0.54^χ
Maternal age	32 (IQR 28–36)	31 (IQR 27–35)	32 (IQR 28–35)	33 (IQR 30–36)	<0.001^t
Marital status
No partner	1200 (13)	713 (18)	330 (11)	157 (6)
With partner	8705 (87)	3237 (82)	2789 (89)	2679 (94)	<0.001^χ
Household social class
Professional/managerial	4872 (48)	1438 (36)	1675 (54)	1759 (62)
Other nonmanual/skilled-manual	3008 (31)	1433 (36)	920 (29)	655 (23)
Unskilled	879 (9)	392 (10)	271 (9)	216 (8)
Never worked at all-no class	1146 (12)	687 (17)	253 (8)	206 (7)	<0.001^χ
Maternal education
Post-secondary	3197 (34)	1621 (41)	975 (31)	601 (21)
Degree	3616 (34)	758 (19)	1246 (40)	1612 (57)
Lower secondary or less	1144 (12)	822 (21)	204 (7)	118 (4)
Non-degree	1939 (20)	746 (19)	692 (22)	501 (18)
Mother return to work (baby's age)	9 (IQR 6–9)	8 (IQR 6–9)	8 (IQR 6–9))	9 (IQR 6–9)
1–5 months	811 (11)	323 (11)	272 (11)	216 (10)
6–7 months	2212 (30)	878 (30)	773 (30)	561 (25)
8–10 months	4693 (60)	1685 (58)	1541 (60)	1467 (65)	<0.001^χ
Maternal health^b
Excellent	2714 (30)	1123 (28)	700 (31)	892 (34)
Very good	3559 (40)	1540 (39)	872 (40)	1149 (41)
Good	2088 (23)	978 (25)	728 (23)	572 (20)
Fair/poor	566 (6)	309 (8)	170 (5)	141 (5)	<0.001^χ
Maternal measured BMI (at interview)	25.4 (4.8)	25.92 (5.1)	25.31 (4.7)	24.83 (4.4)	<0.001^t
Current smoking status
Daily smoker	1663 (17)	1032 (26)	454 (15)	177 (6)
Occasional smoker	741 (7)	314 (8)	286 (9)	141 (5)
Nonsmoker	7499 (76)	2604 (66)	2379 (76)	2516 (89)	<0.001^χ
Ethnicity
Irish	7897 (80)	3739 (95)	2427 (78)	1731 (61)
Other white	1346 (14)	156 (4)	514 (17)	676 (24)
Other^c	624 (6)	49 (2)	164 (5)	411 (15)	<0.001^χ
Maternal stress^d	32 (6.7)	32.26 (6.9)	31.85 (6.7)	31.81 (6.6)	0.8^t
Maternal total depression score^e
No distress	8711 (89)	3397 (87)	2755 (90)	2559 (92)
Psychological-distress	1031 (11)	498 (13)	311 (10)	222 (8)	<0.001^χ
Baby's temperament
Fussy	14 (IQR 11–18)	14 (IQR 11–18)	14 (IQR 11–18)	14 IQR (11–17)	0.35^t
Unpredictable	6 (IQR 4–7)	6 IQR (4–8)	6 (IQR 4–7)	6 (IQR 4–8)	<0.001^t
Unadaptable	8 (IQR 6–11)	9 (IQR 6–12)	8 (IQR 6–11)	8 (IQR 6–11)	0.47^t
Dull	6 (IQR 4–7)	6 IQR (4–8)	5 (IQR 4–7)	6 IQR 4–8)	<0.001^t

Sample description. Number (%), median (IQR), or mean (standard deviation) are shown; ^ap-values are reported for univariate analyses of association for short versus long breastfeeding duration: (^χ- chi-square test; ^W- Wilcoxon rank sum test; ^t- t-test).

Maternal health status as reported by the mother at the time of the interview.

Other includes Chinese/other Asian background; other including mixed background, African or any other black background.

Parental Stress Scale: self reported scale assessing positive and negative aspects of parenthood. Scores are between 18 and 90. Higher scores relate to higher levels of stress.

Center for Epidemiological Studies Depression Scale (8 item). Composite scores range between 0 and 24. Composite scores > = 7 suggest a clinically significant level of psychological distress.

In the LR model, fussy infants had significantly lower odds (OR = 0.98, 95% CI: 0.97–0.99) of being breastfed for 90 days or longer, while unpredictable infants had higher odds (OR = 1.04, 95% CI: 1.02–1.07). The odds of having been breastfed for long duration were also strongly associated (p-value <0.001) with normal mode of delivery, maternal age, maternal smoking status (nonsmoker), maternal higher education, and ethnicity (non-Irish). Single mothers were significantly less likely (OR = 0.58, 95% CI: 0.43–1.08) to sustain breastfeeding for 90 days or longer than mothers who had a partner. A similar trend was observed in mothers with lower secondary education, when compared to mothers educated to degree level (OR = 0.511, 95% CI: 0.375–0.691). Mother's ethnicity (non-Irish) was a strong predictor of longer breastfeeding duration. The results of the POLR model were largely consistent with the results from the LR model. The results of the final multivariable LR and POLR models with breastfeeding duration as outcome variable are presented in Table 2.

Table 2.

Summary of the Association of Breastfeeding Duration Temperament Characteristics (N = 5,955 Infants Where Breastfeeding Was Initiated)

	Logistic regression model		Proportional odds logistic regression model
	Fully adjusted OR (95% CI) for short vs. long breastfeeding duration	p-Values	Fully adjusted OR (95% CI) for the five breastfeeding categories	p-Values
Fussy temperament	0.98 (0.97–0.99)	0.03	0.98 (0.97–0.99)	0.03
Unpredictable temperament	1.04 (1.02–1.07)	<0.001	1.04 (1.02–1.06)	<0.001
Unadaptable temperament	0.99 (0.98–1.01)	0.77	0.99 (0.97–1.00)	0.26
Dull temperament	1.01 (0.98–1.03)	0.4	1.00 (0.98–1.02)	0.55
Sex of the infant
Male	0.92 (0.82–1.03)	0.42	1.06 (0.96–1.17)	0.23
Gestational age	1.04 (1–1.09)	0.09	1.02 (0.98–1.06)	0.19
Delivery mode
Planned/emergency cesarean	0.75 (0.65–0.87)	<0.001	0.78 (0.69–0.88)	<0.001
Suction/forceps assisted/vaginal breech	0.7 (0.6–0.82)	<0.001	0.71 (0.62–0.82)	<0.001
Maternal age	1.32 (0.95 1.84)	<0.001	1.04 (1.03–1.06)	<0.001
Marital status
With partner	1		1
No partner	0.58 (0.43–0.78)	0.001	0.7 (0.55–0.87)	0.002
Household social class
Professional/managerial	1		1
Semiskilled/unskilled manual	0.85 (0.67–1.09)	0.04	0.79 (0.6–1.05)	0.11
Other nonmanual/skilled-manual	0.92 (0.79–1.07)	0.14	0.89 (0.64–1.07)	0.16
Never worked at all-no class	0.85 (0.61–1.2)	0.37	0.95 (0.73–1.24)	0.72
Maternal education
Degree	1		1
Non-degree	0.64 (0.55–0.74)	<0.001	0.62 (0.54–0.70)	<0.001
Post-secondary	0.56 (0.48–0.65)	<0.001	0.55 (0.48–0.62)	<0.001
Lower secondary or less	0.49 (0.37–0.67)	<0.001	0.53 (0.41–0.67)	<0.001
Maternal return to work (baby's age)	1.06 (1.03–1.09)	<0.001	1.08 (1.05–1.1)	<0.001
Maternal BMI (time of interview)	0.97 (0.96–0.98)	<0.001	0.97 (0.96–0.98)	<0.001
Maternal smoking status
Daily	1		1
Not at all	1.66 (1.34–2.06)	<0.001	1.37 (1.16–1.62)	<0.001
Occasionally	1.11 (0.82–1.5)	0.47	1.08 (0.86–1.36)	0.48
Maternal ethnicity
Irish	1	<0.001	1
African or any other black background	7.99 (5.64–11.5)	<0.001	6.67 (5.08–8.8)	<0.001
Any other white background	2.64 (2.25–3.1)	<0.001	2.58 (2.26–2.96)	<0.001
Chinese/other Asian background	3.11 (2.29–4.28)	<0.001	3.15 (2.40–4.15)	<0.001
Other: including mixed background	3.66 (1.73–8.33)	0.001	2.78 (1.52–5.18)	<0.001
Maternal stress score	0.99 (0.98–1.0)	0.1	0.99 (0.98–1)	0.41
Total depression score	0.98 (0.96–1.0)	0.15	0.99 (0.97–1)	0.12

Discussion

This cross-sectional study set out to examine the relationship between infant fussy temperament and breastfeeding duration in a cohort of 9-month-old Irish infants. Our findings suggest that fussy temperament is associated with short breastfeeding duration and that more unpredictable infants are breastfed for longer than 90 days.

Fussy temperament

Shorter exposure to breast milk for fussier infants observed in this study is consistent with the findings of a previous large-scale study, carried out in Norway, which reported an inverse relationship between difficult temperament and exclusive breastfeeding at age 6 months.²⁵ Similar associations were also observed in a longitudinal study carried out by Vandiver et al. reporting correlations between infant easy temperament and longer duration of breastfeeding and later weaning off.²² Few smaller studies reported on temperamental differences between breastfed and bottle-fed infants, showing associations between irritable temperament and bottle-feeding.^18,19,37

However, some other studies found no associations between the type of feeding and infant temperament^30,38–40 or indeed report opposing results.²⁴

Unpredictable temperament

To our knowledge, this is the first study reporting the positive association between infant unpredictability and longer breastfeeding duration. Infant unpredictability, as defined by the ICQ-6, is reflective of how difficult it is to predict infant's needs and this might interfere with establishing a routine. It is possible that the mothers of unpredictable infants were determined to develop a more relaxed dyadic interaction and to improve on their ability to adapt to the daily routine changes inherent to mothering a young infant. Greater maternal flexibility/adaptability has been previously linked with increased breastfeeding duration.^10,11 It might be that infant unpredictability led to mothers becoming more adaptable facilitating longer breastfeeding. It is also possible that the close bond formed between mother and infant during breastfeeding gives the mothers of unpredictable infants a sense of control that might be generally lacking due to increased unpredictability. This might further lead to a stronger desire to continue breastfeeding for longer duration.

The findings of this research study have a bivalent meaning and importance. First, it is suggested that difficult infants may be deprived of the benefits of longer breastfeeding. Second, these findings suggest that breastfeeding cessation may also be modulated by infant temperament characteristics. This is not surprising as previous studies support the important role played by infant temperament in attaining synchronicity within the mother–infant dyad, suggesting that infant temperament might influence maternal decisions during postnatal period. This influence might be exercised through a direct pathway, as it is possible that fussing and crying are mistaken with hunger, which might be further interpreted as insufficient breast milk leading to breastfeeding cessation. Previous research cited “faith in the natural superiority of breastfeeding” and “breastfeeding self-efficacy” as two of the “top 5” factors that play a determinant role in breastfeeding duration, stating that mothers who are concerned about the quality and quantity of their breast milk might resort to the certainty and control that formula products offered.^10,11 The negative effect of infant difficult temperament might also be exercised through an indirect pathway represented by changes in the goodness-of-fit within the mother–infant dyad leading to increased stress and anxiety and possibly reducing the mother's confidence in her mothering abilities.

It is possible that early breastfeeding cessation is a sign of difficulties in understanding the reason for fussy infant behavior. The existent literature shows that children with more difficult temperament are more challenging to care for, posing feeding difficulties, including food refusal.^41–44 It has also been previously reported that fussy infants are more likely to be introduced to complementary food before the age of 4 months²⁸ and that fussing and crying can be easily mistaken by mothers with hunger, prompting them to introduce solids too early.^21,26,27 In this context, setting one-size-fits-all, across the board expectations of breastfeeding duration, might not be a realistic approach and could lead to increased maternal frustration and guilt.

Strengths and limitations

The strengths of this study include the large number of participants (approximately 12.5% of all born in Ireland between December 2007 and June 2008), the use of a validated screening device to determine the dimensions of the infant temperament, and the complexity of information collected in the GUI that enabled us to control for a large number of potential confounders.

Information regarding breastfeeding practices was reported by the mother retrospectively when the infants were 9 months old, however, this is proven to be reliable within the first three years of infant's life.³

Similarly, the assessment of the infant difficult temperament relies on maternal report, recorded when the infants were 9 months old. Reports on infant temperament from previous months (i.e., 3 and 6 months) would have brought further benefits to this study by allowing longitudinal investigation of infant temperament development in relation to breastfeeding status. However, infant temperament (difficult temperament in particular) has proven stability during infancy and early childhood, therefore, we consider that fussy and unpredictable temperament at 9 months is consistent with infant difficultness in previous months.

Conclusions

Infant fussy temperament may have a negative effect on breastfeeding duration. Both mothers and infants might benefit from interventions targeted at improving maternal understanding of infant's fussing or crying behavior while emphasizing the multiple benefits of breastfeeding. Further research investigating how infant unpredictability influences the mother–infant interactions might help in understanding the positive relationship of this temperamental trait and breastfeeding duration. Longitudinal and contemporaneous assessment of infant temperament, maternal psychological factors, and breastfeeding status would help explain the inter-relationship between the three. In addition, longitudinal assessment of maternal expectations regarding both infant temperament development and breastfeeding experience (i.e., breastfeeding expectations, planned duration of breastfeeding) would allow a deeper insight into the psychology of breastfeeding. Infant temperament may influence breastfeeding continuity either directly or indirectly by modulating maternal psychology; therefore, it is important to consider this when analyzing behaviors from the first few months of postnatal life.

Footnotes

Acknowledgment

I acknowledge the work of the Growing Up in Ireland team in collecting and coding the data.

Disclosure Statement

No specific funding has been awarded for this project. No conflict of interest exists.

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