Psychological factors of pregnant women associated with inadequate maternal weight gain in Japan

Abstract Objectives Inadequate gestational weight gain (GWG) has been associated with low birth weight (LBW). However, factors associated with inadequate GWG in Japan remain unclear. Here, we aimed to determine the factors associated with inadequate GWG and the characteristics of inadequate GWG based on the pre-pregnancy body mass index (BMI) among pregnant women in Japan. Methods This observational study included pregnant women at ≥16 weeks of gestation. The study was conducted at two general hospitals in Tokyo, Japan. The participants were requested to complete a questionnaire during the antenatal checkup visit and a mail survey after childbirth. Data were also collected from medical records. The GWG level and associated factors were assessed using the chi-square test or t-test. Results In total, 252 pregnant women were recruited and completed the questionnaires. Data from 128 pregnant women were analyzed. Overall, 23 (18.0%) women were classified as having inadequate GWG. The factors associated with inadequate GWG were as follows: pre-pregnancy underweight, hospital admission owing to hyperemesis, low body esteem, high Edinburgh Postnatal Depression Scale score, low target GWG, more significant weight loss during pregnancy when compared with that pre-pregnancy, high maximum weight loss during pregnancy, delay in return to pre-pregnancy weight, lower birth weight, and inadequate GWG perception. Pregnant women with inadequate weight gain did not receive any medical advice to avoid being overweight but were rather advised to gain additional weight. Conclusion Target GWG and low body esteem were associated with inadequate GWG and other factors that could be modified. Medical staff should focus on achieving the target GWG and improving the body appreciation level among pregnant women.


Introduction
In Japan, the rate of low birth weight (LBW; <2,500 g) has increased from 4.9% in 1985 to 9.6% in 2010 [1]. It should be noted that this rate is higher than that reported in other high-income countries [2]. A previous epidemiological study in the United Kingdom reported that LBW increased the risk of heart disease and mortality rates during adulthood, which is well known as the "Developmental Origins of Health and Disease" theory [3]. Inadequate gestational weight gain (GWG; maternal weight gain during pregnancy) is an important factor that leads to LBW [4,5]. Therefore, weight management during pregnancy is crucial for improving the long-term health of children.
Previous studies have revealed factors associated with inadequate GWG, including low income and multiparity [6,7]. However, compared with other countries, Japan may exhibit distinct factors associated with inadequate GWG. Considering non-pregnant Japanese women, a body mass index (BMI) <18.5 is prevalent among 21.7% of women in their 20's and 13.4% in their 30's [8]. This finding is likely attributed to the current societal standards for female beauty, whereby thin women are considered beautiful [9,10]. In addition, Japanese women are likely to overestimate their body size [11], and even pregnant women experience body dissatisfaction and a desire to remain slim [12].
Furthermore, certain restrictions are aimed at preventing maternal weight gain [13]. Under these circumstances, pregnant women implement measures to prevent weight gain. Thus, inadequate GWG in Japan may be associated with unique factors. In addition, the medical staff cannot effectively support pregnant women who gain less weight than the current recommendations. Moreover, the Japanese guidelines do not provide concrete advice to pregnant women who gain less weight than the current recommendations.
A scientific behavioral approach has recently been implemented to facilitate individual health behavioral changes. The health belief model (HBM) is a conceptual behavioral change theory frequently used in public health, focusing on individual health behaviors [14,15]. Several previous studies have applied this theory for weight management among other patient groups [16,17], while one study has applied this theory to prevent excessive GWG [18].
The HBM has four health belief domains: perceived susceptibility, perceived severity, perceived benefits, and perceived barriers. There is a high probability of adopting a healthy behavior when individuals' "perceived susceptibility, severity, and benefits" of such behavior are more substantial than the "perceived barriers." Individual characteristics and psychosocial factors can impact health beliefs. In addition, the perceived ability to act ("self-efficacy") and the possibility to alter one's behavior ("cue to action") influence the likelihood of adopting a healthy behavior. Understanding the beliefs of pregnant women in Japan regarding GWG based on the HBM framework may facilitate the provision of adequate support to this patient group.
In the present study, we aimed to examine the psychological factors associated with inadequate GWG and determine the characteristics of inadequate GWG based on the pre-pregnancy BMI levels among pregnant women in Japan. Two hypotheses need to be addressed: (1) perceived severity of inadequate GWG is negatively associated with inadequate GWG, and (2) low body esteem is positively associated with inadequate GWG.

Study design and participants
This prospective observational study was conducted at two general hospitals in the urban area of Tokyo, Japan, between July and November 2019. The characteristics of users were similar between the two hospitals. Pregnant women were recruited during an antenatal checkup visit at participating hospitals. The inclusion criteria for study participation were singleton pregnancy at 16 weeks of gestation and the ability to read Japanese text. This gestational age was selected because most women at this point in pregnancy experience a decline in symptoms such as nausea and vomiting, which frequently results in increased appetite and physical activity. Herein, we were interested in factors that lead to inadequate GWG despite the ability to consume food.

Procedures
While awaiting antenatal checkups, consenting participants were requested to complete questionnaires, which included questions on explanatory and psychological variables (Time 1: T1). The participants who could not complete the questionnaires during the hospital visit were allowed to take the questionnaires home and complete them. The questionnaires were then returned at the next checkup visit or by mail. Childbirth data were collected by researchers reviewing the hospital medical records or by employing a mail survey (Time 2: T2). Some participants delivered their babies at other hospitals not involved in the survey. In such cases, the childbirth data could not be collected by reviewing the medical records. Hence, the childbirth data were obtained through a mail survey.
Data regarding gestation and delivery were collected from medical records (T1 and T2). Data on height, pre-pregnancy weight, weight changes during pregnancy, weight at the last antenatal checkup visit, gestational weeks at birth, pregnancy history, medical history, and childbirth were obtained from the medical records. "Weight changes during pregnancy" were used to assess weight change during pregnancy when compared with the pre-pregnancy weight.
Women with a pre-pregnancy BMI of 25 kg/m 2 , who experienced preterm birth, with excessive GWG, and with no childbirth data were excluded. In Japan, individuals with pre-pregnancy obesity are instructed to avoid gaining excessive weight during pregnancy, given that pre-pregnancy obesity is a risk of pregnancy-related complications. Accordingly, we believe that the reasons underlying poor weight gain during pregnancy differed between individuals who were underweight or had normal body weight pre-pregnancy and those who were obese pre-pregnancy.

Variables
Outcome variables GWG was calculated by subtracting the pre-pregnancy weight from the weight at the last antenatal checkup visit. Based on the pre-pregnancy BMI, the participants were classified as exhibiting inadequate (underweight: GWG <9 kg, normal: GWG <7 kg), adequate (underweight: 9-12 kg, normal: 7-12 kg), or excessive (underweight and normal: GWG >12 kg) weight gain based on the dietary guidelines established by the Ministry of Health, Labor and Welfare Japan (MHLW) in 2019 (Table 1) [19]. GWG was not adjusted for gestational age at delivery.

Behavioral variables
The intention of weight management. Data on the target GWG (set by pregnant women) and thoughts regarding weight control during pregnancy were collected.
Behavior. Data on behaviors to control possible weight gain were collected. The questions addressed high/low-calorie food intake and physical activity. Each question was rated as increasing/decreasing/intention not to change/do nothing. Participants with answers other than "do nothing" were considered to have taken action to control their weight.
HBM. Participants' health beliefs regarding GWG were collected using an original questionnaire based on the HBM constructs (susceptibility, severity, benefits, barriers, and self-efficacy). To evaluate the participants' perceived susceptibility, participants were asked, "Do you think you will gain excessive weight by the time of childbirth?/Do you think you will have lower weight gain by the time of childbirth?" Six items were developed to assess the perceived severity (e.g. "How much do you care about you and your baby if your GWG is minimal?") and benefits (e.g. "How much do you think about you and your baby, if you control your weight during pregnancy?"). Each item was rated on a fivepoint Likert scale ranging from "I think so" to "I do not think so." Two questions, answerable as "yes" or "no," were used to assess the perceived barriers (e.g. "Do you think that you manage your food intake/physical activity for weight control during pregnancy?"). A scale was used to assess self-efficacy for healthy eating [20]; this scale has 20 items and six subscales. Each item was rated on a five-point Likert scale ranging from 1 to 5, and the total scores ranged from 9 to 45. The Cronbach's a coefficient in this study was 0.925.

Psychological variables
Body Appreciation Scale-2 (BAS-2). This scale is used to comprehensively assess positive body image [21,22] and consists of 10 items (e.g. I respect my body). Each item is rated on a five-point Likert scale, from 1 (not at all) to 5 (always). The total score ranges from 10 to 50, and higher scores indicate acceptance of one's body. The Cronbach's a coefficient in this study was 0.920.

Mother-to-Infant Bonding Questionnaire (MIBQ).
This scale assesses the emotional relationship between the mother and baby during the antenatal period [23].
It is used to screen for fetal bonding during pregnancy and postpartum [24] and includes nine items. Each item is rated on a four-point Likert scale ranging from 0 to 3, with reverse scoring of some items. The total score ranges from 0 to 27. A higher score indicates worse mother-to-infant bonding. The Cronbach's a coefficient in this study was 0.651.

Sense of Coherence-3 (SOC-3). SOC-3 assesses an
individual's health maintenance and stress-coping ability [25]. Low SOC is associated with distress and depressive symptoms. This scale includes three items [26], rated on a seven-point Likert scale ranging from 1 to 7; a higher score indicates higher coping ability. The total scores ranged from 3 to 21. The Cronbach's a coefficient in this study was 0.822.

Edinburgh Postnatal Depression Scale (EPDS).
This tool comprises ten questions to screen for postpartum depression in the previous seven days [27,28]. In addition, it is used to assess for antenatal depression [29]. Each question was rated on a four-point Likert scale, ranging from 0 to 3. The total scores ranged from 0 to 30. Higher scores indicate more severe depressive symptoms. The Cronbach's a coefficient in this study was 0.764.

Physical variables
Using an original questionnaire, participants were asked if they had experienced nausea and vomiting and, if so, were required to detail their symptoms: (1) nausea, upset stomach, (2) vomiting, (3) loss of appetite, (4) cravings, and (5) other.

Sociodemographic variables
The following demographic data were collected using questionnaires or from medical records: age, parity, educational attainment, annual household income, smoking and alcohol consumption before and during pregnancy.
The following childbirth data were collected from the medical records or by e-mail: gestational age at birth, newborn sex, birth weight, birth height, birth chest circumference, and birth head circumference.

Ethical considerations
This study was approved by the Ethics Committee of the Graduate School of Medicine at the University of Tokyo (no. 2019080NI). The study procedure was explained to all participants. Written informed consent was obtained from all participants.

Statistical analysis
The association between sociodemographic and behavioral variables and attitudes toward weight gain was assessed using the chi-square test or Student's ttest, as appropriate, to determine the associated factors. Missing values were excluded for each analysis. All statistical analyses were performed using SPSS version 25.0 software for Windows (IBM Corp., Armonk, NY, USA). The threshold of significance was p < .05.

Participant's characteristics
A total of 252 pregnant women were recruited, and 227 (90.1%) provided written informed consent and completed the questionnaire at T1. No women experienced gestational diabetes mellitus or hypertensive disorders related to pregnancy. In addition, no women had smoked or consumed alcohol during pregnancy. Finally, 174 birth records were obtained from the T2 group.
For analyses, we excluded participants (n ¼ 46) with a pre-pregnancy BMI of 25 kg/m 2 (n ¼ 10), who delivered at <37 weeks of gestation (n ¼ 3), had excessive GWG (n ¼ 32), or were outliers and had unrealistic GWG (n ¼ 1). Thus, we analyzed the data of 128 participants. Table 2 summarizes the characteristics of participants in the inadequate and adequate GWG groups. Pregnant women were classified as having inadequate (n ¼ 23, 18.0%) or adequate (n ¼ 105, 82.0%) GWG. Women with inadequate GWG had significantly low BAS-2 scores; that is, a low level of body acceptance was significantly associated with inadequate GWG. Although not pathological, a high EPDS score is also associated with inadequate GWG. The incidence of weight loss during pregnancy, compared with that pre-pregnancy, was 65.2% among women with inadequate GWG. Moreover, 55.1% of women desired to gain the recommended weight.
Factors associated with inadequate GWG according to the pre-pregnancy BMI Table 3 presents the characteristics of participants in each weight gain level based on the pre-pregnancy BMI. Considering the pre-pregnancy underweight group, women who experienced significantly greater weight loss than pre-pregnancy weight had inadequate GWG compared with those who did not experience greater weight loss than pre-pregnancy weight. Among women in the pre-pregnancy normal weight group, the factors associated with inadequate GWG were low target GWG, a lack of advice regarding "avoid becoming overweight" from the medical staff, advice from the medical staff to "gain more weight," losing more weight during pregnancy than pre-pregnancy, and delayed return of body weight to pre-pregnancy levels. Overall, 75-80% of women had a personal target GWG in the inadequate GWG group. Approximately 50-55% received advice from medical staff, although only 15-20% of women received specific GWG values. Nearly 63-67% of women with inadequate GWG lost more weight during pregnancy than the pre-pregnancy body weight, returning to pre-pregnancy weight around 21-22 weeks gestation. Lower birth weight tended to be associated with inadequate GWG, although this finding was non-significant owing to the small sample size.

Discussion
To the best of our knowledge, the present study is the first to report on factors associated with inadequate GWG based on the HBM. Considering the hypotheses, we observed that (1) a perceived severity of inadequate GWG was not associated with inadequate GWG, and (2) low body self-esteem was positively associated with inadequate GWG.

Participants' characteristics
Herein, 13.4% of participants had inadequate GWG (23/171, excluding those who delivered at <37 weeks of gestation). This prevalence rate was lower than that reported in a previous study, which showed an inadequate GWG rate of 21.7% and categorized GWG based on the MHLW guidelines among Japanese women [30].  .

Target GWG
The target GWG in the inadequate GWG group was lower than that of the adequate GWG group. The inadequate GWG group may have established a target GWG lower than the recommended value. A previous study has suggested that Japanese pregnant women tend to be concerned regarding weight gain during pregnancy and seek advice from healthcare providers to limit their GWG [31]. Pregnant women in Japan tend to believe that it is favorable to restrict body weight gain. Moreover, a previous study reported that pregnant Japanese women tend to overestimate their body size [12]. Considering the accumulated evidence, pregnant women in Japan may be excessively strict in maintaining their body size and may restrict themselves from gaining weight. The medical staff needs to focus on target GWG in pregnant women to prevent inadequate GWG.

Psychological factors
Low body esteem during pregnancy was associated with inadequate GWG. Body appreciation is defined as "accepting, holding favorable opinions toward, and respecting the body while rejecting media-promoted appearance ideals as the only form of human beauty" [32]. A low acceptance of one's body was significantly associated with inadequate GWG. This evidence might influence the GWG target setting, given that pregnant women in Japan might excessively restrict their weight if they do not respect their bodies. High EPDS scores are also associated with inadequate GWG. Loss of appetite is a known symptom of depression. Thus, medical staff should establish body image perception and depression before advising a pregnant woman on weight management.

Health belief model
The HBM proposes that "perceived susceptibility" increases the implementation of healthy behaviors. However, a high perceived susceptibility to inadequate GWG contributed to the inadequate GWG in the present study; this finding could be attributed to most participants being recruited during the third trimester. Accordingly, only a brief pregnancy period was to be completed, and body weight could not be increased despite recognizing its importance. Therefore, the causal relationship was reversed in this study. An early pregnancy study might reveal whether the HBM can be applied to achieve weight control during pregnancy.
Characteristics of inadequate GWG according to pre-pregnancy BMI Weight loss during pregnancy Among women in the inadequate GWG group, 65.2% experienced more significant weight loss during pregnancy than that pre-pregnancy. Typically, the frequency of nausea and vomiting decreases at the beginning of the second trimester of pregnancy [33]. However, some pregnant women experience nausea and vomiting until the end of the third trimester. Pregnant women might lose their appetite if nausea and vomiting persist for an extended period, given that abdominal enlargement occurs owing to the growing fetus during the third trimester [34]. Therefore, it may be difficult for women to gain weight. A Japanese guideline suggests that pregnant women with obesity pre-pregnancy gain 0.3-0.5 kg per week after the second trimester. However, recommendations for women who experience weight loss during pregnancy are yet to be established. Further research is needed to determine the risks associated with rapid weight gain during pregnancy among women experiencing weight loss.
Advice from the medical staff Furthermore, the present study highlights two important points. First, approximately 75-80% of women have a personal target GWG (Table 3), and 55% of all women agree to gain weight as recommended by the health worker (Table 2). Therefore, these women have a personal target GWG of approximately 8-9 kg (2nd  line Table 3), and women with adequate GWG achieve these targets (9-10 kg, Table 3). Hence, the majority of pregnant women comply with the recommendations. However, only 15-20% of pregnant women were recommended specific GWG values despite 50-55% receiving advice from medical staff (Table 3). This is an important point of progress in the management of pregnancy: from the first prenatal visit, specific GWG values must be systematically presented to women.
Second, 62% of women with inadequate GWG experienced weight loss during pregnancy and did not regain their pre-pregnancy weight until around 21-22 weeks of gestation (Table 3). Medical staff must follow up with pregnant women experiencing considerable weight loss, such that their body weight is less than their pre-pregnancy weight.

Limitations and strengths
This study has several limitations. First, the study sample size was small. The results could not identify factors associated with inadequate GWG or control for confounding factors. Second, the HBM had reversal causes and affected the results, given that the duration between T1 and T2 was short. The pregnant women's beliefs regarding susceptibility likely reflected their situation during the period. Susceptibility should be assessed earlier, such as during the first trimester. Further research should consider surveying women during the early stages of pregnancy to more accurately determine any association between health beliefs and health-promoting behaviors. Third, weight at the last antenatal checkup was selfreported by participants who delivered at nonparticipating hospitals. Social desirability response bias may have occurred because of the increasing adequate GWG rate. In addition, there is a major discrepancy between the self-completed questionnaires and information collected from the medical records.
Despite these limitations, this study has several strengths. The present study was the first to report the association of target GWG and low body esteem with inadequate GWG among Japanese pregnant women. These findings suggest that medical staff should explain the risk of inadequate GWG and the importance of weight gain during pregnancy and discuss potential weight gain weight strategies with pregnant women.

Conclusion
In Japan, low target GWG and low body esteem might be associated with inadequate GWG in pregnant women. When providing health guidance to pregnant women with insufficient GWG, health professionals should evaluate the nutritional status and their target GWG.