Birth Stress and Self-Reported Sleep Difficulty

Transcription

1 Sleep, 8(3): Raven Press, New York Birth Stress and Self-Reported Sleep Difficulty Stanley Coren and * Alan Searleman Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada; and *Department of Psychology, St. Lawrence University, Canton, New York, USA Summary: Difficulty in falling asleep and frequency of night wakenings were assessed in 1,272 college-aged individuals for whom birth histories (based on retrospective maternal reports) were available. A history of birth complications was associated with reports of sleep difficulties as an infant. Birth stressors, such as breech birth, prolonged labor, low birth weight, and multiple births, were predictive of disrupted sleep patterns in the young adult. Key Words: Birth stress-sleep difficulty. Research on insomnia has focused primarily on the current physiological and psychological status of patients rather than on their developmental histories. Little attention has been given to the possibility that the adult sleep problems may have had their genesis much earlier in the individual's developmental history, perhaps even in infancy. Birth complications have been implicated in some forms of infant sleep disturbance, such as night waking. For example, when labor was prolonged 0), birth weight was low (2), there was maternal alcoholism (3), or mild anoxia at birth (4), infants tend to show disrupted sleep patterns. Such early disturbed sleep patterns often persist through the first 14 months of life (5). There has been a further suggestion that children who suffered mild anoxias at birth may demonstrate hypermotility and impulsiveness well into the school years (6). One might well ask whether these effects of birth stressors persist into adulthood, perhaps manifesting themselves in apparently normal populations as some form of insomnia. To answer this question, we conducted the following study. METHOD Over the past several years samples of freshmen students enrolled in the University of Victoria and the University of British Columbia have completed surveys to assess their sensorimotor status. A subsection of the survey used included self-report measures on the quality of sleep. The questions asked focused on whether the individual had "trouble falling asleep" or a tendency to "wake frequently." Each question was scored on a five-point scale, with the following choices of answers: "never," "seldom," "sometimes," "often," and "always." A total of 3,923 subjects were thus assessed. Next, the family of each of the subjects Accepted for publication April Address correspondence and reprint requests to S. Coren at Department of Psychology, University of British Columbia, Vancouver, B.C., Canada. 222

2 BIRTH STRESS AND ADULT SLEEP 223 was contacted by mail to obtain information on birth patterns associated with all the children in the family. Specifically, each mother was asked to complete a questionnaire that asked whether there were any complications or difficulties encountered in the delivery of each of her children. The specific birth stressors listed on the questionnaire were "premature birth," "prolonged labor," "breech birth," "blue-baby or breathing difficulties," "low birth weight," "Caesarean delivery," "multiple births (i.e., twins or triplets)," and "Rh incompatibility." This method of assessing birth trauma in college-aged subjects has been successfully employed in a number of studies (7-9). In addition to information pertaining to possible birth stressors, mothers were also queried as to whether there were any manifest sleep difficulties for each of her children when infants. It was hoped that by seeking information on all offspring, we would place no implicit pressure on the mother to provide positive instances of problems for the child who was actually targeted for this research. These procedures resulted in a final sample of 1,272 individuals (593 men, 680 women) for whom maternal reports of birth circumstances and early sleep history, as well as self reports of current sleep patterns, were available. RESULTS AND DISCUSSION Since the return rate from the maternal information survey was not 100%, it was important to ascertain whether the sample of mothers whose maternal reports were received differed in any systematic way from the sample of mothers that did not respond. No significant demographic differences existed between the respondent and nonrespondent samples in terms of the targeted child's sex (53 versus 54% female, respectively), age (mean age for both was 18.6 years), race (sample was limited to Caucasians), or socioeconomic status (head of the household was college educated for 32.1 and 29.6% of the samples, respectively). Most importantly, the samples seemed to be equivalent in terms of the variables under consideration, with individuals who reported that they always or often have trouble sleeping making up 7.2% of the sample for which maternal reports were available, as opposed to 7.4% of the sample for which the mothers did not provide birth data. A similar pattern prevailed for subjects always or often having night wakenings (8.8 and 8.4%, respectively). Thus it seems unlikely that there was any systematic bias in the pattern of returns that would be of relevance to the variables under consideration. As noted, some reports have suggested that birth stressors, including long labor (1), low birth weight (2), and mild anoxia (4), tend to disrupt sleep patterns in the infant. The maternal reports on the presence or absence of birth stressors and on the presence or absence of sleep difficulty in the proband, when an infant, made it easy to assess whether this previously reported pattern was replicated in the present sample. Furthermore, they provided some indication as to which specific birth stressors are most apt to induce these infant sleep disruptions. To obtain an overall view of the relative contribution of birth stress to infant sleep difficulty, we dichotomously scored the presence or absence of birth stressors and maternal reports of infant sleep difficulty. Fourfold point correlations (Table I, first column of figures) were then computed from these dichotomous data. These correlations may be interpreted in the same manner as Pearson product moment correlations (from which they are derived). As can be seen from Table I, for five of the eight birth stressors we found significant relationships between reports of sleep difficulty and maternal reports of birth stressors. The highest degree of association between birth stress and maternal recollection of infant sleep difficulty is found for breech birth, followed in decreasing order by low birth weight, Sleep. Vol. 8, No.3, 1985

3 224 S. COREN AND A. SEARLEMAN TABLE 1. Correlations between self-reported sleep problems in collegeaged adults and the presence of potential stressors at birth (n == 1,272) Birth stressor Premature birth Prolonged labor Breech birth Breathing difficulty Low birth weight Caesarean section Multiple birth Rh incompatibility ap < bp < ep < Adult self-reported sleep Maternal report...;p:...r_ob_l_em_s of infant sleep Trouble Night problems falling asleep wakening e 0.45ge e e e 0.141e e e a 0.141e e e a e b a e Number of subjects with stress multiple birth, Rh incompatibility, and prolonged labor. It thus seems clear that a number of birth stressors do predict the presence of sleep difficulties in the infant, at least according to retrospective maternal report. Overall, these results tend to replicate earlier reports of sleep difficulties in infants with birth stress, and to indicate that the relevant stressors are not limited only to low birth weight, but include also prolonged labor, breech birth, multiple birth, and Rh incompatibility. Before we address the issue of birth stress and adult sleep problems, it seems reasonable to ask whether infant sleep difficulties predict a pattern of sleep disruption in the adult. The answer involves a comparison between maternal reports about infant sleep difficulties and present self reports by the college-aged probands. Adult subjects used a five-point scale to rate two aspects of their sleep behavior (i.e., trouble falling asleep and frequency of night wakenings). For the purposes of this analysis individuals who reported that they never or seldom had trouble falling asleep formed a single normal sleep group, while those who responded that they sometimes, often, or always had trouble falling asleep formed a disturbed sleep group. These two groups were then compared with the maternal reports of disturbed infant sleep. The results were quite striking. Of those individuals whose mothers reported that they had experienced disrupted infant sleep patterns, 18 years later we found that 77.3% reported that they presently have difficulty falling asleep. In contrast, of the group reported as having no infant sleep difficulties, only 37.2% reported having any trouble falling asleep as young adults [X 2 (1) = 41.91, P < 0.001]. A similar pattern emerged for reports of frequent night awakenings. Of individuals who manifested early childhood sleep disruptions, 73.9% report that they are currently bothered by frequent wakenings, whereas only 37.8% of those who had no early childhood history of sleep difficulties reported problems in this regard as adults [X2(1) = 33.22, P < 0.001]. The theoretical significance of these results is that there appears to be a strong relationship between infantile sleep patterns and the patterns of sleep found in the adult. An individual with an early history of sleep difficulty is about twice as likely to manifest sleep difficulty in later life than is an individual who did not experience early sleep difficulties. This key finding suggests that sleep patterns persist over a sizable portion of the life span. Since, as we indicated earlier in this section, there seems to be a relationship between infant sleep

4 BIRTH STRESS AND ADULT SLEEP 225 patterns and the presence or absence of birth stressors, it is reasonable now to analyze the subjective ratings of sleep quality in adults in comparison also with the presence or absence of birth stressors. The second and third columns of figures in Table 1 show the correlation between the eight birth stressors and the adult self reports of difficulty falling asleep and frequency of night wakenings. A fairly consistent pattern emerges from these data. Ofthe 16 correlations, 13 are both positive and statistically significant, indicating greater sleep disturbance in individuals who have been exposed to birth stress. There are some interactions between the two measures of sleep quality and the specific birth stressors. Overall, difficulty falling asleep is more intimately associated with birth stress, with seven of the eight correlations showing a significant effect, as compared with only six of eight for night wakenings (only Caesarean delivery showed a slight reverse effect). Furthermore, the correlations between the presence of a birth stressor and disruption of sleep are higher for difficulty falling asleep than for frequency of awakening. The largest effects appear for breech births, followed by multiple birth and low birth weight, respectively. Premature birth and Rh incompatibility show significant effects only on the adult's ability to fall asleep; they have no apparent effect on night wakenings. The overall pattern of results seems to provide a clear link between the presence of birth stressors and adult self reports of disrupted sleep patterns. The fact that maternal reports of infant sleep problems predict later self reports of recurrent difficulty falling asleep and frequent night wakenings suggests that tendencies toward insomnia may be part of a lifelong pattern. These tendencies may have a partial genesis in slight traumas incurred as a result of minor stresses associated with the intrauterine environment or the delivery process itself. These would result in a persistent pattern of hyperarousal that manifests itself as difficulty falling asleep or increased frequency of awakening persisting into adulthood. These results are consistent with the notion that a difficult birth or an unusual intrauterine environment may stress the fetus sufficiently to produce a disruption or alteration of the neural maturational pattern. If the stressor is mild enough, the resultant changes could be quite SUbtle, in the sense that the individual would not show any overt disorder save some disorganization in sleep pattern. Sleep difficulties may thus be visible behavioral markers of minor deviations in neurological development. Individuals with such markers might well be suffering from some covert trauma that does not render them manifestly abnormal, but rather alinormal (ali- meaning "elsewhere" or "otherwise") suggesting that except for deviations from statistically observed norms, gross inspection does not reveal any readily manifest abnormality. Sleep disruption is not the first minor behavioral deviation to be predicted by the presence of birth stressors. A growing body of evidence (7-10) suggests that left-handedness and deviations from standard handwriting postures may also arise as subtle consequences of similar birth stressors. Again, such sinistrality shows up as a deviation from the population norm, rather than as an overt instance of abnormality. These data have both substantive and methodological implications. In the substantive realm they indicate that early events, especially those associated with the intrauterine environment and the birth process, may be important factors in determining the sleep pattern in the adult. An individual who has been exposed to some form of birth stress is much more likely to show disorganized sleep patterns, both as an infant and as a mature person than is a nonstressed individual. These data further illustrate that sleep patterns established in infancy may predict sleep patterns in the adult. The sleep-disturbed infant is apt to grow up to be a sleep-disturbed adult. From a methodological perspective, these

5 226 S. COREN AND A. SEARLEMAN findings emphasize the importance of early developmental or physiological factors in the etioiogy of a life history of disorganized sleep patierns and insomnia. Acknowledgment: This research was supported in part by grants from the National Science and Engineering Research Council of Canada and from St. Lawrence University. We gratefully acknowledge the contribution of Dr. Clare Porac, who has been associated with this project since its inception, both in data collection and in preparation of early drafts of the manuscript. REFERENCES 1. Bernal IF. Night waking in infants during the first 14 months. Dev Med Child Neurol 1973;15: Bhatia VP, Katiyar OP, Agarwal KN, Dey PK. Sleep cycle studies in babies of undernourished mothers. Arch Dis Child 1980;55: Rosett HL, Snyder P, Sander LW, et al. Effects of maternal drinking on neonate state regulation. Dev Med Child Neurol 1979;21: Moore T, Ucko LE. Night waking in early infancy. Part 1. Arch Dis Child 1957;32: Richards MPM, Bernal IF. An observational study of mother-infant interaction. In: B1urton-lones N, ed. Ethological studies of child behavior. London: Cambridge University Press, 1972: Rosenfeld GB, Bradley C. Childhood behavior sequelae of asphyxia in infancy. Pediatrics 1948;2: Coren S, Porac C. Birth factors in laterality: effects of birth order, parental age and birth stress on four indices of lateral preference. Behav Genet 1980;10: Coren S, Searleman A, Porac C. The effects of specific birth stressors on four indexes of lateral preference. Can J Psychol 1982;36: Searleman A, Porae C, Coren S. The relationship between birth stress and writing hand posture. Brain Cognit 1982;1: Porac CP, Coren S. Lateral preferences and human behavior. New York: Springer-Verlag, 1981.