Iodine status and knowledge among pregnant and lactating women in Large City in Northern China after nearly 30 years of the universal salt iodization.

Background: With the implementation of the universal salt iodization, the iodine nutrition for children and adults has been appropriate, but pregnant women are still at risk of iodine deficiency. It is of great public health significance to explore the iodine status and knowledge, and influence factors and the appropriate health education methods among pregnant and lactating women.

Methods: From January 2022 to December 2023, at least 50 pregnant women and 50 lactating women were randomly selected from the resident population annually in 16 districts of Tianjin, North China. A total of 1671 pregnant women and 1658 lactating women were recruited. All participants' households salt and random urine samples were collected. A questionnaire was conducted to collect data on iodine related knowledge and behaviors as well as needs of health education from all participants. Logistic regression models were constructed to analyze the factors affecting the iodine related knowledge level. We used the Rasch model and the quadrantal graph to analyze the participants' knowledge level on different iodine-related questions and their needs for health education.

Results: The median urine iodine concentration (UIC) of pregnant and lactating women in Tianjin were 152.40 μg/L and 124.60 μg/L. In some districts, the median UIC of pregnant and lactating women below the appropriate range. The iodized salt coverage rate of pregnant and lactating women in Tianjin was 76.12% and 77.40%, respectively. In pregnant and lactating women who did not actively supplement with iodine, the median UIC in those who consumed non-iodized salt were significantly lower than that in those who consumed iodized salt (139.26 μg/L and 154.40 μg/L, P = 0.044; 94.60 μg/L and 123.80 μg/L, P < 0.001). Compared with the low knowledge score group, pregnant women in the high knowledge score group had a higher proportion of iodized salt consumption (71.25% and 78.05%, P = 0.003), and pregnant and lactating women in the high knowledge score group had a higher proportion of actively supplement iodine (44.61% and 55.34%, P < 0.001; 39.26% and 49.78%, P < 0.001). Health education may be the main factor affecting the iodine related knowledge scores for pregnant and lactating women, with adjusted odds ratios (OR) and 95% confidence intervals (CI) of 2.89 (2.30, 3.62) and 2.46 (1.97, 3.07), respectively. Pregnant and lactating women are most expected to acquire knowledge through healthcare professionals (72.11%) and wechat/website (74.91%), respectively.

Conclusions: Pregnant and lactating women in some areas of Tianjin are at risk of iodine deficiency. Iodized salt consumption is an important way to ensure iodine nutrition of the population, and the lack of iodine related knowledge is an important factor affecting the consumption of iodized salt. Health education in different ways can be carried out for different people to improve the acceptance and efficiency of health education.