Infant night waking linked to postpartum depression

The concept that increased night waking is an evolutionary development allowing for improved survival in those babies who wake more frequently is an interesting idea but is not proven by this study, which suffers from significant limitations given the underlying study design.

As a cross-sectional survey, this study can demonstrate correlation but not causality. The best conclusion this study can reach is that there is a link between the incidence of PPD and the frequency with which a woman’s child is waking in the night. Whether a woman is more likely to be depressed if her child is waking more frequently or a child is more likely to wake frequently if his mother is depressed cannot be determined. Additionally, the validity of this link is limited by recall bias. In this case, a woman with depression may be more likely to remember the past week in a negative light and thereby overestimate the number of times her child woke in the night then a non-depressed woman would. Considering these limitations, this study ultimately only shows a possible correlation between infant night waking and maternal depression.

As with most mental health conditions, PPD is all-too-often overlooked. There is much to be learned about PPD and I am grateful to Gunst et al for their efforts in this field. However, I do not find any significant new understanding of this disease is gained from this project. What is more, I worry for the emotional ramifications of implying to a woman with PPD that her baby’s best interests are pitted against her own and that it is her baby who is responsible for her depression. I would argue strongly against disseminating the study’s findings as anything more than interesting ideas.

Gunst and colleagues attempt to shed light on a functional or adaptive reason for why PPD occurs. The hypothesis is that an infant’s behavior, including nursing and waking in the night, strains the mother. The maternal strain is presumed to decrease the likelihood that she has another child within a near time frame (eg, while the current infant is still young). The presumed adaptive aspect of this is that it would secure more maternal resources (eg maternal time and physical energy) for the infant rather than the maternal resources being shared between the infant and a younger sibling.

While the study was not designed to directly test whether a subsequent pregnancy was, in fact, delayed in association with a baby’s night waking and overall nursing, the authors did examine whether maternal fatigue was related to baby night wakings and overall nursing. The study further examined whether maternal fatigue was associated with PPD. Not surprisingly, maternal fatigue was associated with baby night wakings. Maternal fatigue was also associated with scores on a PPD measure. This finding is consistent with what has been learned in prior studies. The authors also found breastfeeding was associated with lower postpartum depression scores. This stands in contrast with other studies that have found that women breastfeeding have higher depression scores and that breastfeeding is not protective against depression symptoms.

The lack of consistent conclusions regarding breastfeeding and PPD creates a challenge for counseling patients. Perhaps the more important counseling regarding breastfeeding is to consider whether the infant’s health is significantly associated with formula use or breastmilk. When researchers have controlled for the socioeconomic status variables of the mother and family, the health outcomes of formula fed children do not differ from the health outcomes of breastfed children. With this in mind, if breastfeeding is impairing sleep and increasing fatigue for the mother, medical professionals may choose to counsel the mother to make choices that prioritize her sleep. This would be expected to promote a more positive mood state for the mother.

Importantly, a relationship between sleep disruption/fatigue and poor mood is not exclusive to PPD. Rather, it is well-established that fatigue and poor sleep are associated with worsened mood, heightened anxiety and irritability and impaired concentration and attention. All medical providers should be advising patients to get sufficient sleep and certainly, this advice applies to women in the postpartum time frame. Women with infants, however, can struggle to follow this advice. Social narratives regarding so-called good mothering often imply that caring, nurturing mothers put their baby’s needs ahead of their own, including sleep. Consequently, if a woman does try to enact strategies to increase her sleep, such as infant sleep training or enlisting others to care for the baby in the night, it can challenge her self-assessment of her mothering.