Sleep problems and problems in rhythmicity are multiply determined, and are known to be influenced by several factors including in utero exposures of several types(37
), such as prematurity(38
), and feeding schedule(39
). Findings from this large-scale community study indicate that variation in sleep difficulties at 18 and 30 months is associated with prenatal maternal anxiety and depression. This finding was robust, that is, evident at successive assessments, and evident even after controlling for obstetric outcome and psychosocial risk and multiple
measures of post
natal depression and anxiety. The findings support considerable animal evidence and extend limited human data showing that prenatal factors may have persisting influences on sleep in the child.
Before considering the scientific and clinical implications of the work, we first note some limitations of the study. Assessing sleep using maternal report is an established methodology, particularly for large-scale studies, and the measure used here assessed sleep behaviors that are widely assessed in survey studies; however, this measure may not index the same kinds or degree of problems as laboratory measures. In the absence of a priori hypotheses about particular forms of sleep problems, we defined a broad sleep problem phenotype. We cannot determine whether or not children who exhibited problems on this scale are at risk for discrete sleep disorders and parasomnias, but the prediction of the most widely reported sleep problems means that these findings carry clinical meaning. Reliance on maternal report also raises concern about rater bias inflating the link between prenatal mood and infant sleep; however, the inclusion of multiple postnatal measures of depression and anxiety substantially undermines this explanation. Also, we did not have a direct index of the putative mediating mechanism implied by the animal work, namely, HPA axis functioning. Accordingly, this findings needs to be followed up with smaller laboratory investigation that incorporates biological mechanisms. Set against these limitations are several important strengths of the study, including a prospective longitudinal design, a large community sampling frame, and multiple measures of maternal mood and infant/toddler sleep.
Animal investigations have demonstrated that early experiences influence the development (e.g., establishment) of the 24-hour diurnal pattern to the HPA system(40
). Parallel evidence in the human is limited, although several possible prenatal risks for the child’s sleep have been suggested(41
). Findings from the current study build on the animal work and extend previous human studies. Our use of a conservative analytic strategy (e.g., covarying multiple measures of post
natal maternal mood) provided particular leverage in testing the hypothesis that there is something particular about prenatal anxiety and depression that confers risk for sleep disturbance in the child. The finding that this association persisted across two occasions of measurement implies that the effect is not transient; quite how enduring the effect is requires further follow-up study.
Further human research that incorporates a direct index of the mediating mechanism implied in animal work, namely the action of glucocorticoids, is important for at least two reasons. First, several studies report a link between the establishment of a diurnal pattern in cortisol and sleeping through the night in infancy(44
). The measure of sleep disturbance used in this study was somewhat broad, but consistent with, and incorporated signs of, a delayed onset of consolidated sleep at 18 and 30 months. It may be that exposure to prenatal maternal anxiety/depression and the implied associated increased exposure to glucocorticoids(45
) disrupts the onset of a normal diurnal pattern and a normal sleep cycle in the child. Further research along these lines also needs to consider how this process may be coordinated with the development of the suprachiasmic nucleus, a key contributor to circadian rhythmicity. Second, it remains to be seen if the sleep problems observed here can account for the reported behavioral and emotional and cognitive problems previously linked with prenatal maternal anxiety, presumably also through disturbance in the HPA axis. Research of that kind might provide one etiological explanation for why sleep and behavioral disturbances covary across development (8
). Research into prenatal mood disturbance and sleep problems may also contribute to the growing interest in the links between sleep quality and general health outcomes, and the possibility that there may be fetal origins of a variety of health outcomes(48
The current findings do little to resolve lingering questions about timing
Alongside these positive findings, several non-findings may also be of some interest. It is an interesting developmental point that, at a period at which sleep is not yet consolidated in all infants, there was no link with prenatal mood. Variation in sleep “problems” (e.g., awakening in the night) at that early period are not uncommon and may reflect normative variation in the consolidation of sleep. Also, in later assessments, which took place long after the expected onset of consolidated sleep, the amount of sleep remained strikingly unrelated to prenatal mood, and was non-significant even in a sample of many thousand children. These observations provide important clues to clarifying which sleep phenotypes may be most profitable to study in further research.
One intriguing hypothesis that needs testing is that prenatal intervention to reduce anxiety and depression may have beneficial carry-over effects for the baby, including sleep. Evidence-based psychological interventions may carry special advantages for women in pregnancy given the concerns about the use of drug treatment in pregnant women(49
). Studies of sleep-disturbed children often find evidence of co-occurring maternal depression(50
) or relationship difficulties(51
); significantly, the treatment of these disturbances have been shown to improve the young child’s sleep(52
). Research on the effects of prenatal treatment of maternal mood disturbance on infant/toddler sleep is needed before the clinical implications of the current results can be fully understood.