Sleep Measured by Inlab Polysomnography

There is agreement within the professional sleep community (American Sleep Disorders Association 1997) of a pregnancy-associated sleep disorder, however much of the data are inconsistent and contradictory. The discrepancies stem primarily from changes in technology and in the understanding of sleep over the past several decades. Early studies were able to suggest only crude estimations of sleep changes due to limitations of the EEG recording equipment used (Branchey and Petre-Quadens 1968; Karacan, Heine, and Agnew 1968), while recent studies are able to delineate more accurately between stages of sleep and analyze data more in depth via spectral analysis (Brunner, Munch, Biedermann, Huch, Huch, and Borbely 1994). Despite the current technological sophistication and an expansion of neuroscience, data from the last 35 years are still being corroborated today. In 1968, Branchey and Petre-Quadens conducted one of the earliest studies objectively using PSG to assess sleep architecture in pregnant women. Approximately 57 nocturnal sleep recordings were conducted on 17 pregnant women. The overall results revealed an increase in paradoxical sleep (analogous to REM sleep) at 25 weeks of pregnancy with a "clear-cut" decrease in the final 3 to 4 weeks of pregnancy (Branchey et al. 1968). Another study by Karacan et al. (1968) investigated sleep patterns during late pregnancy and showed sleep to be markedly altered during the last trimester of pregnancy even with a small, homogenous population (all middle-class Caucasians). Corroborating their initial study, Karacan et al. (1968) further demonstrated that sleep onset latency (SOL) was considerably longer and the number of awakenings was higher in women during the last month of pregnancy compared to controls, while a complete reduction in Stage 4 sleep was seen in 57% of the subjects (Karacan et al. 1968; Karacan, Williams, Hursch, McCaulley, and Heine 1969). These sleep disturbances were greater than previously reported. Additionally, the authors state that sleep disturbances could "profoundly affect the woman's physiological disposition, perhaps to the point of inducing disease" (p. 933), suggesting over 30 years ago the association between pregnancy-related sleep disturbances and immune dysregulation.

Recent PSG studies have extended and clarified the initial findings of the 1960s. Hertz, Fast, Feinsilver, Albertario, Schulman, and Fein (1992) evaluated 12 women in their third trimester of pregnancy and 10 age-matched nonpregnant controls. One night of PSG revealed that pregnant women had increased WASO and awakenings, increased %Stage 1 sleep and decreased %REM sleep compared to controls. Considering sleep across pregnancy, Driver and Shapiro conducted PSG studies in five women during each trimester and found significantly longer time spent awake following an arousal as the pregnancy progressed (Driver and Shapiro 1992). They also reported that slow wave sleep (SWS) was increased, with increased Stage 4 sleep from the first trimester to second as well as first to third trimester. Similar to the Branchey and Petre-Quadens' results, a significant decrease in rapid eye movement (REM) sleep was observed during the same time frames, unfortunately, Driver and Shapiro failed to report which week of pregnancy the women were studied. Similar to the study conducted by Driver and Shapiro, Brunner et al. (1994) investigated PSG sleep during the course of pregnancy in nine women for two consecutive nights during each trimester. Unlike the Driver and Shapiro (1992) study, the time frame of gestation in which data were collected was narrower and defined; for example, the third trimester recordings occurring during weeks 32 to 35. And unlike Branchey and Petre-Quadens (1968), no data were collected during the final few weeks of pregnancy. Despite these methodological differences, results were comparable with increased WASO mostly in the third trimester, and decreased REM sleep over the course of the pregnancy. More recently a PSG study of four pregnant women carried out by Schorr, Chawla, Devidas, Sullivan, Naef, and Morrison (1998) reported that pregnant women experienced less SWS than the nonpregnant women, but unlike the previously mentioned studies, no differences in REM sleep were noted among or between the groups. Unlike the Driver et al. study, there were no differences seen across pregnancy, only when compared to controls. These studies confirm that physiological sleep is disturbed during pregnancy and that the degree and type of disruption depends on the trimester and/or week of pregnancy.

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