Among the women in early pregnancy, the total daily smartphone viewing time was the longest in the three types of electronic screen exposure. Moreover, we suggested that total daily smartphone viewing time, smartphone and television viewing time before nocturnal sleep were associated with depression among women in early pregnancy, and the thresholds were 7.5 hours/day, 1.5 hours/day and 1.5 hours/day, respectively. Women with higher scores of smartphone addiction were more susceptible to depression.
According to the previous and current studies, the exposure time of smartphone screen has been getting longer among pregnant women in China. A cross-sectional survey[8] conducted in 2015 indicated that 62.6% pregnant women reported mobile phone viewing time ≥ 1 hour/day. However, our previous study[9] carried out in 2019 showed that, the median using time of smartphones among healthy pregnant women was 5.5 hour/day. The present study was conducted in 2022, and indicated the median viewing time of smartphone among women in early pregnancy was 5 hour/day. The longer exposure time of smartphone might result from the widely use of 4G/5G network and various applications (APPs) with plural functions. Nevertheless, our studies were all located in south Jiangsu province, which could not represent all the districts in China.
It has been well demonstrated that overuse of smartphone or smartphone addiction is significantly related to depression among university students[16–18] and adults[19], which is consistent with the results of present study. The accurate mechanisms remained unclear, whereas the prolonged sedentary time might play an important role in the relationship between smartphone overuse and depression. As sitting hours increased, university students’ stress, anxiety, and depression significantly increased despite controlling for sex, economic level, body mass index, underlying disease, and health self-management[20]. A meta-analysis indicated that screen time accounted for 57.2% of total sedentary time in adults during the COVID-19 pandemic, and increases in sedentary time were negatively correlated with global mental health, depression, anxiety and quality of life, irrespective of age[21]. Therefore, total daily smartphone screen time and sedentary time should be kept within reasonable limits.
Exposure to electronic screens before nocturnal sleep was particularly related to depression among women in early pregnancy, which should be paid more attention to. People with smartphone addiction were inclined to postpone their bedtime[22]. If individuals use smartphones in low light conditions, the blue light generated from smartphones would significantly decrease sleepiness and confusion-bewilderment[23]. However, short sleep duration was established as a risk factor of depression[22, 24] in adults. Hence, screen time before nocturnal sleep should be strictly controlled.
In spite of the hazardous effects of prolonged screen time, electronic devices are irreplaceable in modern life, and it is necessary to determine the appropriate threshold time for the target population. In our study, the thresholds of total smartphone viewing time, smartphone and television viewing time before nocturnal sleep were calculated as 7.5 hours/day, 1.5 hours/day and 1.5 hours/day, respectively. Although the AUCs were all less than 0.6 and Youden Indexes were around 0.1, the specificity of total smartphone viewing time and television viewing time before nocturnal sleep was 0.795 and 0.882, respectively. In other words, women with screen time below those thresholds might not be depressed. Still, the conformation of thresholds should be warranted by more large scale and multi-center studies.
Besides the exposure time of smartphone, the usages might be also correlated with depression in women during early pregnancy. The top three smartphone usages (excluding “Others”) in women with depression were watching videos (22.0%), listening to music (20.9%) and playing games (16.7%). Although these results were concluded from descriptive analyses but not statistical inferences, it could be supported by other researches. Among Korean middle school students, the order of the usage types with the highest influence on smartphone addiction was: enjoying music/videos, social network service, and study[25]. A large-scale cross-sectional study suggested that social media and video games was related to the symptoms of psychiatric disorders, including anxiety and depression[26]. Nonetheless, the mechanism of the relationships between different smartphone usages and depression were unknown.
Finally, we didn’t find any statistical significance of computer screen exposure. Since a variety of computer functions can be replaced by smartphones, people tend to use smartphones more frequently. As a result, computers were used mainly for work by most women, whereas only 29.8% were only for entertainment. Then, the exposure hours of computer were fewer than those of smartphone, especially before nocturnal sleep. So, the computer screen exposure might not be a risk factor for women in early pregnancy.
Limitations were also existed in our study. Firstly, the electronic screen time was self-reported by participants, resulting in the inaccuracy hours of screen time. Secondly, the present study was a cross-sectional study, and the evidence power was limited. Finally, the thresholds were calculated for depression, which might not be suitable for other disorders. Given this, a follow-up, cohort study should be conducted.