A Systematic Review of Studies Examining Associations between Sleep Characteristics with Dietary Intake and Eating Behaviors during Pregnancy

Little is known about the association between sleep and diet in pregnancy, despite both behaviors impacting maternal and fetal health. We aimed to perform a systematic review of the available literature on associations between sleep characteristics and dietary intake and eating behaviors during pregnancy, reporting on both maternal and fetal outcomes. We followed the 2020 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and conducted our search on 27 May 2021 in the PubMed, EMBASE, and CINAHL databases. The search yielded 6785 unique articles, of which 25 met our eligibility criteria. The studies, mostly observational, published 1993–2021, include data from 168,665 participants. Studies included examinations of associations between various maternal sleep measures with a diverse set of diet-related measures, including energy or nutrient intake (N = 12), dietary patterns (N = 9), and eating behaviors (N = 11). Associations of maternal exposures with fetal/infant outcomes were also examined (N = 5). We observed considerable heterogeneity across studies precluding our ability to perform a meta-analysis or form strong conclusions; however, several studies did report significant findings. Results from this systematic review demonstrate the need for consistency in methods across studies to better understand relationships between diet and sleep characteristics during pregnancy.


Introduction
Sleep and diet are two important health behaviors that undergo changes during pregnancy and have implications for maternal and fetal health outcomes. Pregnant women report significant changes in their sleep over gestation including a reduction in sleep duration [1,2] and degradation of sleep quality [3], increase in wake after sleep onset, decrease in sleep efficiency, and a higher number of naps [4]. Sleep disturbances, including short sleep duration and poor sleep quality, have been linked to adverse perinatal outcomes such as a higher risk of gestational diabetes, preterm birth, greater gestational weight gain [5], longer labor, and a higher rate of Cesarean delivery [6].
Clinical sleep disorders have also been associated with adverse pregnancy and fetal outcomes. Specifically, restless leg syndrome has been linked to the development of

Data Extraction
All authors participated in data extraction, with two authors independently extracting data from each article in the final pool of studies. We extracted data related to study design, sample characteristics, measures for the variables of interest, and analyses and results related to the relationship of interest, and rated the Melnyk level of evidence for each article based on the analytical approach for the relationship of interest [45]. For example, if the analysis was conducted within the context of a prospective cohort study, but was crosssectional in nature, the article's level of evidence was rated as a 4 as opposed to a 3.

Sleep Variables and Energy Intake
The GUSTO study measured diet with a single 24 h recall during the second trimester among 497 participants of the mother-offspring cohort study in Singapore [66] and the Peking University Birth Cohort measured diet with two non-consecutive 24 h recalls during the first trimester among 4352 participants [54]; neither found an association between energy intake and sleep quality. No association was found between energy intake, calculated based on metabolic parameters and weight (not dietary assessment), with awakenings or sleep duration among 31 overweight or obese participants [46]. Likewise, no association was found between energy intake assessed with two non-consecutive 24 h recalls and nighttime sleep duration among the 3692 participants of the same Peking University Birth Cohort mentioned above [54], and no association was found between energy intake, assessed using a single 24 h recall and nighttime sleep duration or bedtime among 1152 participants of the GUSTO study [60], also mentioned above.
Energy intake among 52 pregnant women with obesity, assessed in the first and third trimesters using energy expenditure (doubly labeled water) and fat deposition (changes in fat density), was not associated with total sleep time [56]. However, women who increased their time in bed were found to have lower energy intake across pregnancy compared to those who decreased their time in bed. Finally, a study of 437 participants in the Australian Longitudinal Study on Women's Health (ALSWH) found that energy intake, assessed at any time during pregnancy using a food frequency questionnaire, was associated with sleeping behavior patterns that were identified via latent class analysis in crude models [49]. Women with average sleep duration and adverse sleep symptoms had higher energy intake compared to those with average sleep duration, but no adverse sleep-related symptoms [49]. These findings did not persist after adjustment for potential confounders [49].
An intervention study providing meal replacement for two meals per day aimed to restrict caloric intake to promote weight control and adherence to guideline recommendations of gestational weight gain [47]. No difference was found in actigraphy-measured sleep duration between the intervention and usual care comparison group [47].

Sleep Variables and Nutrient Intake
The relationship between nutrient intake and various aspects of sleep was also examined. Sleep and dietary fat were assessed by two studies [49,50]. In the first study, wherein 213 pregnant participants were recruited at Special Supplement Program for Women Infants and Children (WIC) sites in Michigan and assessed at a single time point, which included 36% in the first trimester, 32% in the second trimester and 32% in the third trimester. Dietary fat intake, measured by the Block screener was found to be directly associated with nighttime sleep disturbance in the overall cohort (p < 0.01) [50]. However, path analysis examining participants by trimester demonstrated that an association of dietary fat with depression (p < 0.05), and not nighttime sleep disturbance, was found during the first trimester [50]. That same study showed a path connecting sleep latency to dietary fat through the association with both fruit and vegetable intake (p < 0.05 for each leg of the path). Among second-trimester participants, an association of dietary fat with nighttime sleep disturbances (p < 0.01) and with fruit and vegetable intake (p < 0.05) was found, but none of these factors connected to depression [50]. Third-trimester participants were found to have an association between dietary fat and nighttime sleep disturbances (p < 0.05), which was also associated with depression (p < 0.01). An association of monounsaturated fat intake, but not overall fat intake, with sleep patterns was identified, as described above among the ALSWH sample [49]. Women with average sleep who also had adverse sleep symptoms consumed less monounsaturated fat than women with average sleep and no adverse sleep symptoms (p < 0.05) [49].
The relationship between carbohydrate intake and sleep was also assessed in two studies [49,67]. In cross-sectional analyses, the percentage of energy consumed as starch was found to be significantly higher among women with average sleep who also had adverse sleep symptoms, in comparison to women with average sleep and no adverse sleep symptoms (p < 0.05), though no differences in overall carbohydrate intake or sugar consumption were found between sleep pattern groups [49]. However, in multivariate models, overall carbohydrate intake was higher among women with average sleep who also had adverse sleep symptoms, in comparison to women with average sleep and no adverse sleep symptoms (p < 0.05), though no relationship was found for starch or sugar consumption with sleep patterns [49]. In the second study [67], intake of sugar-sweetened beverage, assessed by three 24 h recalls, was associated with short sleep duration and poor sleep quality, even after adjustment for potentially confounding variables. However, this cross-sectional study did not separate sugar-sweetened beverages that did or did not contain caffeine.
Additionally, the GUSTO mother-offspring cohort study in Singapore assessed discretionary calories as the sum of energy from caloric beverages (≥5 kcal; excluding plain water, diet soda, and unsweetened coffee, tea, and cow's milk), local cakes, desserts, and snacks based on 24 h recall data. No association was found between discretionary calories with either sleep quality or duration assessed using the PSQI [66].
Caffeine consumption was assessed with maternal diet in two studies [52,68]. Maternal caffeine consumption during pregnancy was assessed with obstetrical outcomes among 750 participants recruited during the second trimester [52]. They reported that caffeine consumption during the second and third trimesters was associated with higher maternal depression and anxiety scores, and more cigarette use. Controlling for these variables, the investigators found that higher maternal caffeine consumption was significantly related to lower maternal sleep effectiveness as assessed by a Sleep Scale [52]. However, a study of 266 pregnant women in Poland late in pregnancy found no difference in insomnia between participants who did and did not abstain from coffee consumption during pregnancy [68].

Maternal Sleep with Dietary Patterns (N = 9 Studies)
Dietary intake was also assessed as food group consumption or dietary patterns (Table 3) [50,[53][54][55][56][57][58]66,69]. Fruit and vegetable intake among Michigan WIC participants, assessed using a rapid food screener, was associated with sleep latency in the first and third trimester, but not in the second, and no association of fruit and vegetable intake with sleep quality or duration was found in any trimester [50]. In contrast, others assessing US respondents to the Behavioral Risk Factor Surveillance System (BRFSS) found that fruit and vegetable consumption as well as fruit consumption alone were associated with increased odds of meeting or exceeding sleep duration recommendations, but this association was only found when assessing sleep as an ordinal variable, while no association was found in linear models [55]. Several studies also examined associations between sleep and diet quality. Healthy Eating Index was calculated for two studies using very different dietary data collection. Diet was measured among pregnant women with obesity using food photography via the SmartIntake app collected in early (13-17 weeks' gestation) and late (35-37 weeks' gestation) pregnancy [56], whereas diet among women of any weight status was assessed using a single 24 h recall at 24-28 weeks' gestation [66]. The first study using SmartIntake found no significant association between diet quality and time spent in bed or total sleep time [56]. The second that used 24 h recall also did not find an association between diet quality and sleep duration but did find a slightly higher HEI score (higher quality diet) among participants with good quality sleep (54.6) compared with those with poor quality sleep (52.0), though that association was no longer statistically significant when controlling for anxiety [66]. Chronotype (a person's circadian preference in behavioral and biological rhythms relative to the external light-dark cycle) in the first trimester was associated with HEI scores calculated from three 24 h recalls such that higher whole grain and lower fruit HEI sub-scores were associated with higher HEI scores, though no difference in overall HEI score by chronotype was identified [58].
Four studies examined associations between various measures of sleep and several different types of dietary patterns [53,54,57,69]. A Mediterranean food pattern, assessed with a food frequency questionnaire among Spanish women at 11-13 weeks and 34 weeks' gestation, was associated at both time periods with better sleep quality, assessed using the Spanish PSQI. The investigators also examined individual items of the Mediterranean diet, which showed that higher olive oil consumption at both time periods, and fruit early in pregnancy were associated with better sleep quality, while consumption of red meat and sub-products late in pregnancy was associated with lower sleep quality. A prospective study among pregnant Chinese women examined cross-sectional dietary intake and sleep early in pregnancy [53,54]. Dietary intake was measured with two days of 24 h recall from which total caloric intake was calculated, as described previously. However, the authors also categorized participants' diets as balanced, more meat, veggie-rich, or vegan, though no methods for determining these categories were provided. Based on these nonspecific methods, participants described as having a vegetarian or more-vegetables diet type were more likely to have poor sleep quality, as measured by the PSQI, than those with a balanced diet [54]. Additionally, those consuming a vegan diet were more likely to have either short or long sleep duration, which were self-reported. Dietary patterns of pregnant participants during their first trimester of gestation in the Chinese Pregnant Women Cohort Study [69] were assessed by principal components analysis of data derived from a 17-food group-based food frequency questionnaire. These analyses revealed five patterns: plant-based, vitamin-rich, animal protein-rich, bean products, and high fat, which were described by quartiles. Plant-based and vitamin-rich dietary patterns were associated with less sleep disturbance, and a high-fat dietary pattern was associated with greater sleep disturbance [69].

Maternal Sleep with Eating Behaviors (N = 11 Studies)
Eleven studies investigated the association between variables related to maternal eating behaviors with sleep (Table 4) [48,56,58,60,61,[64][65][66]68,70], six of which included a measure related to nighttime eating or fasting [48,58,60,61,66,68]. Among African American women assessed between 14-and 24-weeks' gestation, night eating was associated with lower sleep duration and quality, and higher sleep onset latency assessed using questions from the PSQI [48]. Among 673 s-trimester pregnant women in Singapore, night-eating was associated with a later bedtime, but did not find an association between the number of eating episodes with sleep duration, as reported in response to a single question [60]. The GUSTO mother-offspring cohort study in Singapore found no association between nighttime eating, nighttime fasting interval, and frequency of consumption episodes with either sleep quality or duration assessed using the PSQI [66]. Relatedly, an early pregnancy cross-sectional study in Brazil did not find an association between sleep chronotype and nightly fasting, eating duration, time of first or last meal, and number of meals [58].
Two studies specifically considered the association between nighttime eating and insomnia [61,68]. A study of third-trimester pregnant women in Poland found that women reporting insomnia, using the Athens Insomnia Scale, were more likely to eat at night [68]. Another study of pregnant women in Vietnam from 12 to 33 weeks' gestation found that short meal-to-bed time, based on self-reported times, was a risk factor for reflux-related insomnia [61].
Four studies assessed eating behaviors including binge eating and food cravings [48,56,64,70]. One study of African American women with overweight or obesity between 14-and 24-weeks' gestation found that sleep latency and quality (assessed with PSQI) were associated with overeating episodes, and poor sleep quality was associated with binge eating episodes. However, no associations were found between sleep duration and dietary restraint, overeating, or binge eating episodes [48]. The Norwegian Mother and Child Cohort Study (MoBa), which is a large, prospective population-based cohort study, assessed mothers with binge eating disorder (BED) symptoms and their associations with sleep, which was self-reported as sleep problem occurrence and during which weeks of gestation, sleep duration and satisfaction [65]. Participants reported BED symptoms before and during pregnancy. Participants reporting pre-pregnancy BED that remitted during pregnancy, or those reporting incident BED during pregnancy, were more likely to report sleep problems, and the likelihood of those problems increased with each trimester [65]. Incident BED during pregnancy was associated with both long and short sleep durations, whereas BED symptoms before or during pregnancy, or pre-pregnancy BED that remitted during pregnancy was not associated with long or short sleep. All three BED groups reported higher odds of sleep dissatisfaction than participants without any BED symptoms or history [65].
Food cravings were also examined with respect to sleep in two studies. One study of 52 pregnant women with obesity assessed sleep with wrist-worn actigraphy over six consecutive nights during early and late pregnancy. Pregnant women in this study who increased time in bed from early to late pregnancy also reported an increase in food cravings during that time compared to women who decreased time in bed or those who had no change in time in bed [56]. Another study of 245 pregnant women in Brazil assessed chronotype via mid-sleep time on free days with correction for calculated sleep debt across various times in pregnancy. Participants with sleep chronotype of evening types, which have ≥5 h difference between weekend and weekday average sleep duration, were more likely to report relief from negative states and feelings as a result of eating (as measured by the Food Craving Questionnaire-Trait) than those in non-evening chronotype (<5 h difference between weekend and week day average sleep duration). Compared to participants reporting morning type (<3.59 h difference between weekend and weekday average sleep duration), those with evening type reported both anticipation of relief from negative states and feelings as a result of eating, anticipation of positive reinforcement that may result from eating. Intense desire to eat was more likely to be found among evening type compared with morning type participants, whereas both intense desire to eat, and anticipation of positive reinforcement that may result from eating were found between evening type and non-evening type participants [64]. Additionally, The Pregnancy Eating Attributes Study (PEAS) followed 373 women from early pregnancy to one year postpartum [70]. Eating behaviors measured included cravings, which were assessed using questions developed by the authors wherein participants listed cravings and rated their strength; hedonic hunger, based on the Power of Food Scale; and addictive-like eating based on a modified Yale Food Addiction Scale. Sleep quality, assessed with the PSQI, was associated during pregnancy with cravings frequency and strength, but not with hedonic hunger or addictive-like eating. Additionally, change in sleep quality from pregnancy to post-partum was not associated with changes in hedonic hunger or changes in addictive-like eating [70].

Maternal Exposures with Fetal/Infant Outcomes (N = 5 Studies)
Three studies [51,52,62] examined the associations between maternal caffeine consumption during pregnancy on fetal and/or infant sleep (Table 4) [51,52,62]. The impact of high vs. low maternal caffeine consumption (reported use at study entry of >500mg (N = 10) vs. <200 mg (N = 10), respectively), on fetal behavioral states was assessed throughout the third trimester (30 to 40 weeks of gestational age) [51]. The fetuses of women who reported high caffeine consumption spent less time in active sleep and more time in arousal than fetuses of women with low caffeine consumption [52]. Caffeine consumption during the second and third trimesters was associated with higher maternal depression and anxiety scores, more cigarette use, and lower infant birth weight. Controlling these variables, higher maternal caffeine consumption was significantly related to higher amounts of infant active sleep, and more stress signs, and that caffeine consumption was correlated with lower maternal sleep effectiveness during the first 24 h after delivery [52]. In contrast, the last did not find any significant associations between maternal caffeine consumption during late pregnancy and infant sleep at 3 months of age [62].
One study [63] examined the association between maternal fermented food intake during pregnancy and infant sleep. The investigators found that intake of fermented food, especially miso, during the second and third trimesters, was associated with less infant sleep at one year of age [63].
Finally, another study examined the impact of a maternal sleep-related exposure on an infant diet-related outcome [59]. The investigators found that low maternal sleep efficiency in the third trimester was associated with lower likelihood to initiate breastfeeding, with a trend for a similar association between sleep efficiency and feeding status at 16 weeks postpartum.

Discussion
In this systematic review, we observed significant heterogeneity in studies examining associations between maternal sleep and diet. Differences in existing studies were observed in the selection of exposures and outcomes (sleep vs. diet) and their definitions. Participant samples range in numbers from less than 100 to over 17,000. Pregnant individuals were studied either during a specific trimester, or at any time during pregnancy. Samples also varied in terms of racial and ethnic representation with some studies including participants with a diverse range of demographics, while others included a more homogenous sample. Studies also varied in specific population of pregnant individuals assessed with some assessing participants with different weight statuses, or only including those with overweight or obesity pre-pregnancy. Further, the methodology used to examine sleep varied, but consisted of subjective questionnaires for most studies. Dietary variables of interest also varied with some studies examining diet quality and intake while others examined specific nutrient intake, food groups, or dietary patterns. This marked heterogeneity in the existing literature has precluded our ability to perform a meta-analysis of the data or even to form strong conclusions. Like findings from the Pauley et al. (2023) [43] review, our findings support the need for more longitudinal studies and randomized controlled trials. Notably, only two of the selected studies were designed as a randomized controlled trial. Additionally, a large proportion of data was obtained from low-risk samples, impacting the ability to extrapolate to higher-risk populations.
Energy intake was not found to be strongly associated with sleep among pregnant women. Most (5) of the seven studies that examined energy intake and sleep found no association of caloric intake with sleep quality [54,66] or duration [46,53,60]. The only randomized controlled trial of a partial meal-replacement to limit or control caloric intake also found no differences between intervention and comparison group in actigraphymeasured sleep outcomes [47]. Two studies found an association between energy intake with sleep variables, though methods and conclusions were very dissimilar. Women with obesity who increased their time in bed over the course of pregnancy had lower energy intake compared to those for whom time in bed decreased or stayed the same [56]. In another study, women with average sleep duration and adverse sleep symptoms had higher energy intake compared to those with average sleep duration, but no adverse sleep-related symptoms [49]; however, these findings did not persist in multivariate analysis.
Other studies of non-pregnant adults measuring energy intake and sleep duration have consistently shown that short sleep is associated with higher caloric intake, and that hormonal changes associated with short sleep may be responsible for the small changes in energy intake [71]. The set of papers in our review nicely highlights the wide variations in measurement that included first, second, third, or multiple trimesters. Energy intake was assessed using one or two 24 h recalls, a food frequency questionnaire, and several indirect measures using metabolic estimates of energy usage. Additionally, sleep was assessed in these studies as self-reported and actigraphy-measured sleep duration, self-reported sleep quality, and categories of sleep duration and/or sleep quality. So, though no associations were found between energy intake and sleep in these seven papers, the lack of consistency in methods challenges our ability to draw strong conclusions regarding this relationship.
The relationship between dietary fat intake and sleep among pregnant women is not clear from the two studies that examined this relationship. Neither assessment of sleep (pattern vs. sleep duration, quality, nighttime disturbances, latency) nor diet fat (screener vs. food frequency questionnaire) were assessed consistently across these studies. Higher overall dietary fat intake was associated with more sleep disturbance among Michigan WIC participants [50]. Additionally, women who reported average sleep with adverse sleep symptoms consumed less monounsaturated fat than women with average sleep and no adverse sleep symptoms [49]. Studies among non-pregnant adults of dietary fat with sleep outcomes are not common, but have collectively indicated that higher fat intake is associated with short sleep [71], and insomnia [72], and that saturated fat intake is overall negatively associated with sleep wellness [73]. Little to no literature is available to review the relationship between monounsaturated fat and sleep in other study populations.
Findings regarding the association between carbohydrate intake and sleep were scarce and did not support strong conclusions. The two studies that assessed carbohydrate intake showed higher carbohydrate consumption among women with average sleep, but adverse sleep symptoms, compared to those with average sleep without adverse sleep symptoms [49]. Additionally, higher sugar-sweetened beverage intake was associated with short sleep and poor sleep quality, though caffeine consumption was not taken into account [67]. Consistent association between carbohydrate consumption and sleep outcomes has also been inconclusive in studies of non-pregnant adults [73]. Differentiating between types of carbohydrate may shed light on this issue as intake of a high glycemic index diet or glycemic loads have been posited to be associated with higher risk of insomnia [73,74], which may be due to alterations in amino acid balance or a stimulated inflammatory response [74]. Beyond examining single nutrient diet composition, combinations of nutrients, such as high carbohydrate, low fat, have also been considered as potentially important in the relationship between diet and sleep [75].
Caffeine may be the single most studied substance in this literature. Caffeine consumption in our review was associated with lower maternal sleep effectiveness after controlling for depression and anxiety [52], though abstaining from coffee consumption was not associated with insomnia risk [68]. The impact of caffeine consumption on nighttime sleep is also not clear in non-pregnant adults [76,77], due to the cyclical impact of caffeine on performance enhancement and mitigating sleep deprivation and caffeine withdrawal [76].
A variety of dietary patterns were assessed with sleep in nine papers in this review. Higher fruit and vegetable consumption was inconsistently associated with sleep latency in one small study [50] and broadly associated with meeting or exceeding sleep duration recommendations in a larger, population-based study [55]. Higher fruit and vegetable consumption among non-pregnant adults has been consistently associated with achieving recommended sleep in observational studies, though experimental studies have been inconsistent [78].
Broadly assessing diet quality with sleep, HEI was not consistently found to be associated with sleep duration [56,66], but was associated with sleep quality in one study [66], and HEI sub-scores of higher whole grains and lower fruit consumption were associated with chronotype in another [58]. In non-pregnant adults, HEI has also been found to be associated with various sleep outcomes. HEI assessed using two 24 h recalls was significantly lower among short and long sleepers compared to those reporting the recommended 7-9 h of sleep among nationally representative NHANES study participants [79]. Additionally, among NHANES participants, higher HEI is associated with lower risk of sleep disturbance [80]. Broadly, a review of 29 studies indicates that higher dietary quality is associated with better sleep quality [81], though not all studies used the HEI index and methodological inconsistencies limit the strength of the evidence and preclude causal inference, as we have also found.
Other dietary patterns, such as the Mediterranean diet, veggie-rich, meat-based, plantbased, vegetarian, vegan and other descriptors were mixed in association with various sleep outcomes, and inconclusive in our review. Research in non-pregnant populations has found that Mediterranean diet adherence is positively associated with sleep duration and indicators of better sleep quality [82]. Other studies have found changes in eating patterns associated with short sleep [83]. Among 15,199 adult participants of the NHANES from 2005 to 2010, short sleepers were found to eat earlier and later, consume more calories as snacks (than meals) and consume more sugar and caffeine than participants reporting longer sleep [83].
Nighttime eating is associated with misaligned circadian rhythms, or "eating jetlag", which can be associated with positive energy balance and weight gain among shift workers and others who have milder shifts in eating behavior in the general population [84]. The relationship between nighttime eating and insomnia among pregnant women correlates these two nighttime occurrences, but it is unclear if pregnant women who experience insomnia awaken because of hunger, or eat because they were awake [68]. Insomnia has been found to be associated with intake of higher glycemic index (GI) diet in the Women's Health Initiative Observational Study [74], which has been hypothesized to be mediated by inflammation [73,74]. GI, originally defined as the postprandial glucose response to food, [85] is calculated for and summed over all carbohydrate-containing foods [74].
Sleep seems to also play an important role in eating disorders, including BED [86] and BED. For example, a systematic review by da Luz et al. (2023) [87] found that people who binge eat exhibit poorer overall sleep quality compared to people who do not binge eat, and may have more daytime sleepiness, insomnia, and difficulty falling asleep. BED has even been proposed as a possible circadian disorder [88]. More studies of these associations might explain these relationships as well as the findings among pregnant women reviewed here [48,65].
Cravings have been found to be associated with sleep in various non-pregnant populations. Lack of sleep has been found to be associated with cravings among women without obesity [89], and healthy young adults [90]. Food cravings were associated with poor sleep quality among shift-workers [91]. Higher sleep efficiency was found to be associated with lower sweet cravings among adolescents [92]. Chronotype was not associated with food cravings in several studies [93][94][95]. None of these findings are consistent with the associations of time in bed [56] and chronotype [64] with cravings found among pregnant women in this review.
Interpretation of these results must be considered with the limitations of the processes and studies themselves. As mentioned above, 60% of the studies had a low level of evidence (less than level 4) and only two of the studies were RCTs. Additionally, a wide range of methods and outcome measures were used, which limits the conclusions that can be drawn across studies. Further, most of the studies were conducted only with participants with low-risk pregnancies. However, the review of this research was conducted with systematic processes according to the PRISMA framework, so the literature presented is representative of the state of this research.