By employing the MSAS to assess the status of multiple psychosomatic symptoms among women at different gestational stages, we investigated the multidimensional nature of symptoms (e.g., frequency, severity, and distress) and identified four symptom clusters in early pregnancy, along with three symptom clusters and two independent symptoms in late pregnancy. These results provide further evidence for studies in related fields.
In this study, the symptoms with higher symptom scores, frequency, severity, and distress in early pregnancy were nausea, lack of appetite, drowsiness, lack of energy, and vomiting. This result is consistent with those of previous studies, indicating that these symptoms are commonly experienced during early pregnancy(Bai et al., 2016; Chan et al., 2010; Mindell et al., 2015; Wang Lei et al., 2013). This may be related to an increase in the levels of human chorionic gonadotropin (HCG), a decrease in gastric acid secretion, and prolonged gastric emptying time that occurs during early pregnancy(Committee on Practice, 2018). Whereas the symptoms with higher symptom scores, frequency, severity, and distress in late pregnancy were weight gain, difficulty in sleeping, sweating, lack of energy, and dry mouth. Among them, the lack of energy was a common symptom experienced in both the stages, with an incidence of 70.8–79.5%, which is similar to the findings of Beebe et al(Beebe et al., 2017). This may be due to disruption of sleep and insufficient sleep duration during pregnancy(Mindell et al., 2015). In addition, consistent with previous studies, weight gain and difficulty in falling asleep were common symptoms experienced by women during late pregnancy(Beebe et al., 2017). Pregnant women tend to gain weight due to local changes (e.g., foetal growth and development, uterine enlargement, and the formation of placenta and amniotic fluid) and metabolic changes (e.g., water retention, fat deposition, and protein storage)(Sally, dos Anjos, & Wahrlich, 2013; Torgersen & Curran, 2006). In addition, as the pregnancy progresses, the uterus enlarges and gradually presses upward on the diaphragm, causing mechanical changes in the respiratory system (i.e., increase in the tidal volume, decrease in the functional reserve capacity and residual volume), thereby increasing susceptibility to difficulty in breathing and affecting sleep patterns(Nazik & Eryilmaz, 2014; Torgersen & Curran, 2006). Difficulty in falling asleep may be related to foetal movement and specific types of pain commonly experienced during late pregnancy (e.g., leg cramps, lumbopelvic pain or pressure, and restless legs syndrome)(Mindell et al., 2015; Nazik & Eryilmaz, 2014). Moreover, during the gestational period, women's basal metabolic rate (BMR) increases(Lof et al., 2005; Sally et al., 2013), which accounts for dry mouth and sweating in late pregnancy.
To the best of our knowledge, this study is the first to identify symptom clusters in a population of pregnant women. Eventually, four symptom clusters (pregnancy reaction symptom cluster, mood-fatigue symptom cluster, change in libido and food taste symptom cluster, and dry mouth-bloating symptom cluster) were identified in early pregnancy, and three symptom clusters (mood-fatigue symptom cluster, sleep-bloating symptom cluster, and fluid deficiency symptom cluster) and two independent symptoms (pain and weight gain) were identified in late pregnancy.
In early pregnancy, nausea, vomiting, and lack of appetite formed a cluster called the pregnancy reaction symptom cluster. These three symptoms are typically noted during early pregnancy, and the exact underlying mechanism remains unclear. The prevailing opinion is that it is related to the elevation of progesterone during pregnancy, i.e., progesterone can inhibit the smooth muscles of both the pylorus and the small intestine, resulting in reduced contractility of the gastrointestinal tract and decreased intestinal motility(Body & Christie, 2016). The second symptom cluster identified was comprised of feeling nervous, feeling irritable, lack of energy, difficulty in concentrating, and feeling drowsy, and was named the mood-fatigue symptom cluster. Previous studies have indicated that fatigue, anhedonia, and emotional problems, including anxiety and distress are prevalent among pregnant women(Beebe et al., 2017; Verbeek, Arjadi, Vendrik, Burger, & Berger, 2015). Fatigue during the gestational period is associated with the occurrence of emotional problems(van de Loo et al., 2018), which might aggravate fatigue in turn(Giallo, Gartland, Woolhouse, & Brown, 2016; Jiansheng et al., 2019), consequently resulting in a vicious cycle. The third symptom cluster included problems with sexual interest or activity and change in food tastes. By far, there are no other studies that have replicated the symptom clusters, and therefore, we not yet been able to account for the association between the two symptoms in the third cluster. We had expected that the change in food taste might be related to the cluster consisting of nausea, vomiting, and lack of appetite; however, this was simply not the case. Finally, the fourth and last cluster consisted of dry mouth and feeling bloated, which may be the result of gastrointestinal disorders induced by the alteration of hormones(Keller, Frederking, & Layer, 2008).
The first cluster determined during late pregnancy was the mood-fatigue symptom cluster, which included symptoms such as feeling nervous, feeling irritable, lack of energy, difficulty in concentrating, and feeling drowsy, which was also one of the clusters detected in early pregnancy. This indicated that the mood-fatigue cluster persisted during the two periods and that there was an interaction among these symptoms, despite the fact that we could not figure out the causality of them. This finding implies the need to pay special attention to these interrelated symptoms related to mood and fatigue in symptom management during both early and late pregnancy, which would help pregnant women and their families adjust psychologically and physically till the birth of the offspring. The second symptom cluster identified included symptoms such as difficulty in sleeping and feeling bloated. This gathering phenomenon might be attributed to a shared biological mechanism underlying these symptoms. Specifically, in late pregnancy, due to the fluctuations in oestrogen and progesterone and the mechanical effects of uterine enlargement, the transit rate of the small intestine and colon decreases, which results in symptoms of abdominal distension. Simultaneously, owing to the combined effects of these factors, pregnant women often have multiple types of sleeping disorders, such as difficulty in falling asleep and frequent night awakenings(Keller et al., 2008; Nazik & Eryilmaz, 2014). We also identified another symptom cluster consisting of dry mouth and sweating. One might assumption was that the two symptoms are due to increased BMR observed in late pregnancy(Lof et al., 2005; Sally et al., 2013), despite there being no clear reasoning for the coexistence of these symptoms in a cluster. Besides, two independent symptoms, pain and weight gain, were also observed during late pregnancy. As these two symptoms were not incorporated into a certain cluster, this may, to some extent, account for their prominence and independence in late pregnancy, without sharing some common causes or being greatly associated with symptoms in other clusters (they were more weakly connected with other symptoms with respect to correlations and location of the network matrix), which needs to be explored in future investigations.
There are some limitations to our study. Firstly, the subjects of this study were enrolled from only two tertiary hospitals, and the representability and generalisation of the results are somewhat restricted. Secondly, the available data were self-reported by pregnant women, which may have resulted in recall bias. Thirdly, the instrument adopted for evaluating symptom experience was not specifically designed for pregnant women; therefore, several specific types of pain commonly experienced in late pregnancy, such as leg cramps, lumbopelvic pain or pressure, and restless legs syndrome were not described exactly. Future investigations should adopt a more comprehensive and specific tool to assess the studied symptoms. Additionally, to ensure clinical implications and have a manageable number of symptoms for cluster analysis, the clusters were identified by symptoms with a prevalence over 50%; however, it was challenging beyond this to reach consensus on what remaining symptoms should be contained within. Moreover, there is still some debate about the minimum number of symptoms within a symptom cluster, and the more prevalent ones are the two symptoms proposed by Kim et al(Kim, McGuire, Tulman, & Barsevick, 2005). These were also selected in the present study, which might have had an impact on our results. Furthermore, we used three commonly used approaches (i.e., correlation analysis, partial correlation analysis, and HCA) to determine the symptom clusters, which have been applied to head and neck cancer patients with endotracheal tubes and newly diagnosed glioma patients(Coomans et al., 2019; Li et al., 2020). Nonetheless, the identified symptom clusters may differ when other methods (e.g., factor analysis) are utilised. It remains controversy as to which analytical method is optimal.
Despite the limitations mentioned above, our research has significant implications for further clinical practice. The effects of symptom clusters on individuals may be distinct from, or even greater than, the cumulative effects of a single symptom within a cluster; thus, symptom clusters might potentially be more powerful in shaping a pregnant woman's functional status and quality of life. A more in-depth understanding of how these symptoms coexist during the progression of pregnancy could facilitate the design of comprehensive and appropriate healthcare programs to manage symptoms for multiple potential conditions. Future studies are warranted to explore the underlying biological mechanisms of each symptom cluster to diversify our current understanding of this emerging field.