Does Infant Feeding Method Impact on Maternal Mental Health?

Introduction

Postpartum mental health problems are recognized as a major public health concern and are associated with poor outcomes for women and their children and families.^1,2 It is reported that one in five women experiences a mental health disorder during the postpartum period, with problems ranging from depression, anxiety disorders, posttraumatic stress disorder, and obsessive-compulsive disorder to bipolar disorder, schizophrenia, and psychosis.^3–9 Mental health problems arising in the perinatal period may become chronic and carry over to future pregnancies.^10–12 Maternal mental illness can also have adverse effects on the cognitive, social, and emotional development of infants due to impaired maternal–infant interactions.^13–15

Breastfeeding results in improved health outcomes for both infants and mothers.^16–18 Previous studies have shown an association between postpartum depression and breastfeeding. A systematic review of breastfeeding and maternal health outcomes in developed countries has shown that short duration of breastfeeding or not breastfeeding was associated with elevated risk of postpartum depression. ¹⁷ Watkins et al. ¹⁹ found that women with negative early breastfeeding experiences, including breastfeeding pain in the first day, were more likely to experience postpartum depression at 2 months. A quasi-experimental study in Pakistan found that difficulty in breastfeeding at birth was significantly associated with postpartum anxiety and depression. ²⁰ However, little is known of the effects of breastfeeding on other postpartum mental disorders. In addition, the majority of studies providing information related to postpartum depression and breastfeeding used the Edinburgh Postnatal Depression Scale or other self-report measures of postpartum depression, ²¹ whereas mothers with postpartum depressive symptoms do not necessarily have a clinical diagnosis of depression. Of the few studies using clinical diagnoses of mental disorders occurring within the first postpartum year, none has reported an association between infant feeding method and the interval between birth and hospital admission. The objective of this study is to explore the relationship between early breastfeeding experience and clinically diagnosed postpartum mental disorders and to examine associations between early breastfeeding experience and the interval between birth and the first-time hospital admission for mental disorders.

Materials and Methods

Results

There were 186,452 women who were reported to have given birth in NSW, Australia between January 1, 2007 and December 31, 2008. Of these women, 150,343 (80.6%) were reported to be full breastfeeding, and 24,032 (6.5%) were reported to be breastfeeding with formula at the time of discharge from hospital or discharge from care for home births. The “any breastfeeding” rate, which included either “full breastfeeding” or breastfeeding combined with formula, was 87.1%, whereas the non-breastfeeding (infant formula only) rate was 12.9%.

Compared with “full breastfeeding” mothers, mothers who did not breastfeed at the time of discharge from hospital or care for home births were more likely to be admitted to the hospital in the first year postpartum for schizophrenia (adjusted relative risk [ARR]=2.0; 95% CI 1.3, 3.1), bipolar affective disorders (ARR=1.9; 95% CI 1.1, 3.5), and mental illness due to substance use (ARR=1.8; 95% CI 1.3, 2.5). However, non-breastfeeding mothers were less likely to be admitted to the hospital with a diagnosis of anxiety disorders (ARR=0.6; 95% CI 0.5, 0.9) within 12 months after birth (Table 1).

In total, 2,940 (1.6%) mothers were admitted to the hospital for mental and behavioral disorders within 12 months after birth, 1,037 (0.6%) were diagnosed with adjustment disorders, 971 (0.5%) were diagnosed with unipolar depression, and 585 (0.3%) were diagnosed with anxiety disorders. The mean time period before the first hospital admission with a diagnosis of any mental illness was 169 days for “full breastfeeding” mothers, which was 32 days longer than the 137 days for non-breastfeeding mothers (p<0.05). The first hospital admission for diagnoses of anxiety disorder, unipolar depressions, and adjustment disorders occurred earlier (on average, 41, 36, and 31 days, respectively) (p<0.05) in non-breastfeeding mothers compared with full breastfeeding mothers (Table 2). Table 3 show the social and demographic status of mothers with and without hospital admissions for mental illness in NSW for the study interval. The factors in Table 3 are significantly different and were adjusted for the analysis of ARR in Table 1.

Discussion

The “any breastfeeding” rate of 87.1% found in this cohort is consistent with that reported in a previous newborn feeding practices study in NSW. ¹⁸ Breastfeeding rates at the time of discharge are in keeping with the Australian national target of at least 90% of babies being initially breastfed. ²⁴

Psychiatric disorders in the postpartum period are an important public health issue. This study found that approximately one in 60 women who gave birth in NSW between 2007 and 2008 were admitted to the hospital for a mental and behavior disorder at least once within 12 months after birth. This represents a large burden on the hospital system and is a cause of considerable disruption on the families of these mothers. Better maternal mental health outcomes were reported for full breastfeeding mothers compared with non-breastfeeding mothers at the time of discharge from the hospital or discharge from care for home births. Breastfeeding at this time was associated with a decrease in the risk of hospital admission due to mental and behavior disorders, including schizophrenia, bipolar affective disorders, and mental illness due to substance use within the first postpartum year. In addition, fully breastfeeding at the time of discharge delayed the first postpartum admission for unipolar depressions, adjustment disorders, and anxiety disorders.

Although the benefits of breastfeeding are well documented, as are the negative health consequences of postpartum mental disorders, it is unclear whether breastfeeding status influences postpartum mental disorders, or vice versa. Henderson et al. ²⁵ found that postpartum depressive symptomatology was associated with early cessation of breastfeeding. A population-based study for 594 Canadian mothers reported that those with high Edinburgh Postnatal Depression Scale scores at 1 week postpartum were more likely to discontinue breastfeeding at 4 and/or 8 weeks. ²⁶ However, the use of breastfeeding status at the time of discharge in our study minimizes the negative influence of maternal mood on infant feeding outcome. As the median postnatal length of stay for mothers was 3 days in Australia, ²⁷ the breastfeeding status at the time of discharge reflects the early breastfeeding experience in the hospital, rather than the influence of depressive symptomatology. Therefore, the decreased risk of postpartum mental and behavioral disorder admission for full breastfeeding mothers at the time of discharge suggests a protective effect of breastfeeding on postpartum maternal mental health. The findings in our study indicated the directional effect of early breastfeeding experience on maternal mental health outcomes.

This was the first population-based study to evaluate the influence of early breastfeeding experience on the non-admission days of postpartum admission for mental and behavioral disorders. On average, the first postpartum admission for mental and behavior disorders for full breastfeeding mothers occurred 1 month later than for non-breastfeeding mothers. Mothers are vulnerable to a wide spectrum of mental disorders during the postpartum period, which involves the transition to new motherhood and changes in relationships within families. Breastfeeding is a facilitator of mother–infant bonding, which increases maternal satisfaction, decreases negative mood, and reduces perceived stress in mothers.^28,29 These psychological benefits of breastfeeding may help to defer the onset of mental and behavior disorders. Conversely, the delay in psychiatric admission for mothers who are breastfeeding may be associated with a reluctance by the mother to wean (as psychiatric mother–infant admissions are not available to the majority of these families), hence delaying admission for infant feeding reasons.

Limitations of this study include the lack of evaluation of infant feeding methods at regular intervals during the postpartum period. The dataset used for this study was one of administrative perinatal data with limited information on infant feeding method after women were discharged from the hospital or from care for home births. A future cohort study should be conducted to examine the presence of a psychiatric illness during the antenatal period or at the time of delivery, as this could influence the choice of the infant feeding method. Additional information is needed on breastfeeding status at the time of psychiatric admission to suggest the directional effect of breastfeeding and clinical admission for mental and behavior disorders. Mothers who chose not to initiate breastfeeding should be distinguished from mothers who prematurely discontinued breastfeeding owing to low self-efficacy, experiencing breastfeeding difficulties, or having a physiologically insufficient milk supply.

Conclusions

Breastfeeding is associated with a decrease in the risk of maternal hospital admissions for schizophrenia, bipolar affective disorders, and mental illness due to substance use across the first postpartum year. The decreased risk and the delayed admission of postpartum mental and behavioral disorder for full breastfeeding mothers at the time of discharge suggest a protective effect of breastfeeding on postpartum maternal mental health and an effect of early breastfeeding experience on maternal mental health outcomes. If confirmed, these findings have the potential to improve the health of mothers and to reduce health service costs. These findings will need replication with methodologies addressing breastfeeding status at the time of psychiatric admission.