Association of Iodine-Related Knowledge, Attitudes, and Behaviours with Urinary Iodine Excretion in Pregnant Women with Mild Iodine De ciency

BACKGROUND
Subsequent to the implementation of the universal salt iodisation policy, China has all but eliminated the iodine deficiency disorders. However, pregnant women are still experiencing mild iodine deficiency. The present study explored factors that could relate to mild iodine deficiency in pregnant women.


METHODS
In total, 2400 pregnant women were enrolled using a multistage, stratified, random sampling method in Shanghai. Data were collected via a standardised questionnaire. The urine samples and household cooking salt samples were collected for the detection of urinary iodine and salt iodine concentrations.


RESULTS
The median urinary iodine concentration (MUIC) was 148.0 μg L-1 for all participants, and 155.0 μg L-1 , 151.0 μg L-1 and 139.6 μg L-1 in the first, second and third trimesters. The MUIC in the third trimester was significantly lower than that of the first trimester (P < 0.05). The usage rates of iodised salt and qualified-iodised salt were 71.5% and 59.4%, respectively. Iodine-related knowledge score composition ratio was significantly different between the high and low UIC groups (P < 0.05). Participants' MUIC increased significantly with the increases in iodine-related knowledge score (P < 0.001). The third trimester was a significant risk factor for high UIC, whereas high iodine-related knowledge score, actively learning dietary knowledge and having a habit of consuming iodine-rich food were significant protective factors for high UIC (P < 0.05).


CONCLUSIONS
Iodine level is adequate among pregnant women in Shanghai during the first and the second trimesters, although it is is insufficient in the third trimester. Good iodine-related knowledge, attitudes and behaviours are important for pregnant women with respect to maintaining adequate urinary iodine.


Introduction
Iodine is a trace element that is essential for thyroid hormone synthesis, which is required for infants' physical growth and mental development [1,2[. Iodine de ciency leads to a series of adverse results, including endemic goitre and poor physical growth, collectively known as iodine de ciency disorders (IDDs). Severe iodine de ciency in pregnancy is well known to result in adverse childhood outcomes, such as cretinism and mental retardation [3]. In past decades, Questionnaire Survey All participants were required to complete a standardized questionnaire, which included information on their demographics, salt consumption, and iodinerelated knowledge through face-to-face interviews with trained interviewers. Participants' iodine-related knowledge, attitudes and behaviours was measured using a questionnaire with a total possible score of ten points, based on respondents' ratings of the questions. The questionnaire was adopted after ve experts reviewed its clarity and comprehension and agreed on all the items used in the questionnaire. The reliability coe cient of the questionnaire was 0.87, which was considered acceptable. Iodine-related knowledge was expressed as each participant's total score on the questionnaire. All data were reviewed by the local district CDC project team, and the Shanghai CDC project team reviewed at least 5% of the data.
Data collection and analyses of household cooking salt and urine samples More than 50 g of household cooking salt from each subject were collected during the household assessment. And 5 ml of fasting urine All urine samples were temporarily stored in a refrigerator at 4 ℃, then stored in a freezer at -20 ℃ for 12 hours, and nally transported to the testing unit within two weeks. All cooking salt samples were stored at room temperature and transported to the laboratory within one week.
The household cooking salt iodine concentration (SIC) and urinary iodine concentration (UIC) were measured through titration and acid digestion [17,18], respectively, at the Central Laboratory of Shanghai's Municipal CDC and the 16 district CDCs in Shanghai. The internal quality control of the samples for the analyses of the SIC and UIC were provided by China's National Iodine De ciency Disorders Reference Laboratory of the CDC.

De nitions And Classi cations Of Relevant Indicators
Cooking SIC was classi ed into two types based on cooking SIC standards in Shanghai: non-iodized salt (SIC < 5.0 mg/kg) and iodized salt (SIC ≥ 5.0 mg/kg) which included low-iodized salt (5.0 mg/kg ≤ SIC < 21.0 mg/kg) and quali ed-iodized salt (SIC ≥ 21.0 mg/kg).
The usage rate of iodized salt was equal to the percentage of salt with an iodine level ≥ 5.0 mg/kg in all samples.
The usage rate of quali ed-iodized salt was equal to the percentage of salt with an iodine content ≥ 21.0 mg/kg in all samples.
The 'abundant knowledge' group consisted of participants who scored 8-10 points on the iodine-related knowledge questionnaire. The 'general knowledge' group were those who scored 6-7 points on the iodine-related knowledge questionnaire. The 'lack of knowledge' group were those who scored ≤ 5 points on the iodine-related knowledge questionnaire.
Former smokers were participants who smoked cigarettes in the past, excluding those who took a few tentative puffs. Former drinkers were those who usually drank alcoholic beverages during non-gestational periods, excluding those who sipped some wine.
The nutritional iodine status of the pregnant women was determined using the recommended criteria of the WHO/United Nations Children's Fund (UNICEF)/International Council for the Control of Iodine De ciency Disorders (ICCIDD). Insu cient iodine intake was de ned as MUIC < 150 µg/L; adequate iodine intake as MUIC 150-249 µg/L; iodine intake above the requirement as MUIC 250-499 µg/L; and excessive iodine intake as MUIC ≥ 500 µg/L [12].
Because of the high within-person variability of a single spot urine, the WHO programme guide limited the use and interpretation based on single spot urine per participant to population median of a su ciently large group (in general, > 30) [12]. In our study, the sampling error (95% con dence interval (CI) of the MUIC) was considered and calculated using bootstrapping. Pregnant women are divided into 48 units according to the district and trimester. When the upper cut-off level of the 95% CI the MUIC in a unit was higher than 150 µg/L, the iodine status was considered optimal for all pregnant women in this unit, these participants were categorized as high UIC and the others were low UIC.
The de nition of iodine-rich foods, which included kelp, laver, seaweed, and shrimp, was based on the eating habits of Shanghai residents and the food composition tables published in the China Health and Nutrition Survey (19) .

Statistical analysis
Statistical analyses were conducted with Excel (2010 Edition, Microsoft, China) and SPSS (version 21.0, China). Frequency count data are expressed as number and percentage (%), normally distributed data are expressed as mean ± standard deviation (SD), and non-parametric data are expressed as the median (25th percentile, 75th percentile). One-way analysis of variance (ANOVA) was used to compare multiple groups. In pairwise comparisons, homogeneity of variance was tested using the least signi cant difference (LSD) test, and heterogeneity of variance was assessed using Tamhane's T2 test. The Kruskal-Wallis one-way ANOVA was used to compare the non-parametric data of multiple groups. Binary logistic regression analyses were used to explore factors with the potential to predict low UIC. A P-value below 0.05 was considered to be statistically signi cant.

Characteristics of the participants by trimester
A total of 2 400 eligible participants were included in the study. The MUIC was 148.0 µg/L for all participants, and 155.0 µg/L, 151.0 µg/L, and 139.6 µg/L for women in the rst, second, and third trimesters, respectively. A signi cant difference was found in the MUICs at different gestational weeks (P = 0.027). Pairwise comparisons found a signi cant difference only between the rst and third trimesters, with a higher MUIC during the rst trimester; the adjusted P-value was 0.022. A total of 1 715 households used iodized salt as cooking salt, of which 1 426 used quali ed cooking salt. The usage rates of the iodized salt and quali ed-iodized salt were 71.5% and 59.4%, respectively. The mean iodine content in the iodized salt was 23.9 mg/kg. Age, educational status, occupational status, family income during the past year, thyroid disease history, drinking and smoking habits, and iodine-related knowledge were analysed ( Table 1). Comparisons of participants' characteristics by pregnancy trimester revealed a signi cant difference in educational status among the women in the different trimesters (P = 0.005). No signi cant differences in the other characteristics were found. The women were divided into two groups, high UIC and low UIC. Iodine-related knowledge, usage rates of iodized salt, consumption of iodine-rich food within 48 hours of having an on-the spot iodine urine test, and study the dietary knowledge urgently were signi cantly between the two UIC groups (P < 0.05).

The distributions of UICs and MUICs among women with different knowledge scores
The percentages of UICs ranged between 150 and 250 µg/L were 26.1%, 25.8%, 23.1%, for participants in the rst, second, and third trimesters, respectively, and 25.0% for the pooled results (Fig. 1).
The MUICs of the participants, which varied by their iodine-related knowledge scores, were 133.5 µg/L in the 'lack of knowledge' group, 146.0 µg/L in the 'general knowledge' group, and 164.0 µg/L in the group with 'abundant knowledge' (Fig. 2). A signi cant difference was found between the UICs of the three groups and the pooled results (P < 0.001). The adjusted P-values for the pairwise comparisons were 0.046 between the 'lack of knowledge' and 'general knowledge' groups, < 0.001 between the 'lack of knowledge' and 'abundant knowledge' groups, and 0.035 between the 'general knowledge' and 'abundant knowledge' groups. The results showed that the MUIC increased with increases in knowledge scores.
As trimester was found to be a predictor of UIC, we controlled for the impact of trimester on UIC by comparing the groups with different scores in the same trimester. The differences in the MUIC between the groups with different scores in the same trimester were compared using the Kruskal-Wallis test, which found signi cant differences between the groups with different knowledge scores in the rst (P < 0.001) and third (P = 0.012) trimesters. The pairwise comparisons of the groups with different scores in the rst and third trimesters showed a signi cant difference only between the 'lack of knowledge' (P < 0.001) and the 'abundant knowledge' groups (P = 0.009).

Analysis of the factors associated with UIC
Based on the standards of international organizations (WHO/UNICEF/ICCIDD), patients were divided into two groups, high UIC and low UIC. UIC was used as the dependent variable, and the variables that were signi cant in the univariate analysis were used as the independent variables in the binary logistic regression ( Table 2). Variables with multiple classi cations were treated as dummy variables. The results showed four variables in the model: iodine-related knowledge, consumption of iodine-rich food within 48 hours of an iodine urine test, study the dietary knowledge urgently, and the third trimester. Compared to the rst trimester, the third trimester was found to be a risk factor for high UIC (P = 0.016). Abundant iodine-related knowledge versus lack of knowledge (P < 0.001), eating iodine-rich foods within 48 hours of an iodine urine test versus not eating iodine-rich foods (P = 0.046), and study the dietary knowledge urgently versus no study of dietary information (P = 0.002) served as protective factors for high UIC.

Discussion
It is particularly important for pregnant women to have adequate iodine intake, which is not only related to pregnancy outcomes, but also to the mental and physical development of the foetus [20]. Recent, continuous reports have documented iodine de ciency in pregnant women in China [21][22][23]. The Chinese CDC conducted a cross-sectional study on the relationship between thyroid disease and different levels of iodine intake, which indicated low coverage of iodized salt in the coastal cities of China and low iodine concentrations in the environment; the incidence rate of thyroid dysfunction and the UICs showed a Ushaped curve [22]. All these ndings suggest that the iodine status of pregnant women is worthy of attention, especially in regions where both iodine in the drinking water and the usage of iodized salt are low.
Although Shanghai is located on the coast, it is classi ed as an iodine-de cient region because of its low water concentration of iodine. In 2009, a crosssectional survey of 7 904 participants in all districts of Shanghai found that the median iodine concentration in the drinking water was only 12.8 µg/L, which is well below the standard cut-off point of 40 µg/L for iodine-de cient areas. The survey also found that iodized salt was the main source of dietary iodine in Shanghai, accounting for 63.5% [14].
Our study found that the UIC of pregnant women in Shanghai in 2019 was 148.0 µg/L, indicating mild iodine de ciency (100-149 µg/L), according to the WHO recommendations [12]. The results are similar to those of previous Shanghai monitoring reports [14,15]. According to our ndings, trimesters affect the MUIC of pregnant women. The MUIC of the pregnant women in the third trimester (139.6 µg/L) was much lower than that of rst trimester (155.0 µg/L).
Moreover, a 2018 monitoring study in the Zhejiang province of China, which included 8 651 pregnant women, found that trimester was signi cantly associated with low UIC, with the lowest concentration recorded in the third trimester and the highest in the rst trimester [24]. This result is consistent with the results of a study of 2 607 pregnant women in Chongqing, China, an iodine-su cient area, which reported that women in the rst trimester had a signi cantly higher MUICC (189.7 µg/L) than those in third trimester [163.0 µg/L) [25]. Similarly, a cross-sectional study conducted in Australia found women in the third trimester had a signi cantly lower MUIC than women in the rst trimester (119 vs. 161 µg/L) [26]. This nding may be related to the increasing thyroid hormone requirements of the foetus. Before 20 weeks of gestation, the foetal thyroid is not su ciently mature to produce thyroid hormones independently. Therefore, during this period, the foetus depends entirely on the maternal thyroid hormones and iodine supply [27]. After the foetal thyroid matures, thyroid hormone synthesis increases, relying on iodine from the mother [28], which may increase the iodine requirements of pregnant women in the third trimester. Additional interventions, such as encouraging the intake of iodine-rich foods or iodine supplements are important recommendations for pregnant women in the third trimester.
Our study found that iodine-related dietary knowledge plays a vital role in the UIC of pregnant women, as shown in the univariate analysis and the binary logistic regression. The MUIC increased with higher knowledge scores. Although educational status was not signi cant in the multivariate analysis, the scores on iodine-related dietary knowledge suggest that iodine-related health education is likely to be crucial in preventing low UIC, and cannot be replaced by traditional health education. Furthermore, the 'study the dietary knowledge urgently' served as a protective factor for maintaining high UIC, thereby highlighting the importance of iodine-related health education. Nevertheless, 30.3% of the pregnant women in our study lacked iodine-related knowledge, which suggests that the iodine-related health education should be improved. A cross-sectional study on 804 pregnant women from 18 to 44 years of age in 2016 in Oslo, Norway, showed that 74% of them achieved low iodine-related knowledge scores [29]. A similar result was reported in a cross-sectional study of pregnant women living in Northern Ireland; only 20% of the women were aware [30]. The results of a 2019 study of 2 642 pregnant women in Zhejiang province, China, showed a linear upward trend in iodine-related knowledge scores with higher UICs [31]. According to a 2018 cross-sectional study of pregnant women in Istanbul, nutrition knowledge scores were signi cantly higher in the post-test (23.0) than the pre-test (16.0) after the respondents received nutrition education (P < 0.001) [32]. In the follow-up to the present study, we intend to strengthen the focus on nutrition-related knowledge and enhance participants' understanding of IDD in pregnant women.
Our study also found that the consumption rate of iodized salt was only 71.5%, and the consumption rate of quali ed iodized salt was only 59.4%. Despite the low consumption rate of quali ed iodized salt, our study found that 62.8% of pregnant women had consumed iodine-rich food 24 hours to 48 hours before submitting a sample for an on-the-spot urine iodine test, although iodine-rich foods were forbidden 24 hours before the test. This nding may re ect the dietary habits of eating iodine-rich foods in Shanghai. The multivariate analysis also showed that eating iodine-rich food in the 24-48 hours before a urine iodine test, served as a protective factor for maintaining high UIC. Although iodized salt is a good source of dietary iodine, it is not the only one. Therefore, we should not focus excessive attention on its consumption rate; as long as pregnant women eat reasonable amounts of iodine-rich food, they can maintain their UIC at su cient levels. Thus, it should be noted that in the case of low usage of iodized salt, iodine-related health education is vital for the pregnant population to maintain their UIC at su cient levels.

Conclusion
In summary, participants' MUIC was 155.0 µg/L, 151.0 µg/L, and 139.6 µg/L in rst, second, and third trimesters, respectively, which suggests that pregnant women in the third trimester are at risk for mild iodine de ciency. The low consumption of quali ed iodized salt among pregnant women is also a problem in Shanghai. Abundant iodine-related knowledge, study the dietary knowledge urgently, and eating iodine-rich food in the past 24 to 48 hours, had protective effects on the high UIC of pregnant women. Abundant iodine-related knowledge and positive attitudes and behaviours were associated with high urinary iodine excretion. Therefore, it is important to improve iodine-related health education for pregnant women in Shanghai. The health education should focus on third-trimester pregnant women and on guiding those who eat non-iodized salt to choose reasonable amounts of iodine-rich food.
Declarations Figure 2 Distribution of urinary iodine status by the total knowledge scores of the participants.(LK = lack of knowledge, GK = general knowledge, and AK = abundant knowledge)