Iodine nutrition status among pregnant women before and after adjustment of salt iodine content in Hangzhou City

Objective To explore the impact of iodine nutrition on pregnant women before and after adjusting the iodine content in iodine salt. Methods Twelve counties (areas, cities) in Hangzhou were divided into urban, suburban and rural areas before and after adjusting the iodine content of salt. One survey spot was selected in each district and one hundred pregnant women were selected; family salt and urinary samples of each pregnant woman were collected. The levels of salt and urinary iodine were measured by the methods of picric sodium thiosulfate titrimetric (GB 13025.7-2012) and spectrophotometer (WS/T 107-2006), respectively. Results One thousand two hundred and thirty-nine and one thousand two hundred and thirty-three household salt samples were collected before and after adjusting the iodine content in iodine salt. The median of salt iodine of pregnant women (23.30 mg/kg) before adjusting the iodine content in iodine salt was lower than that after adjusting the iodine content in iodine salt (30.09 mg/kg, χ2=-4.71, P < 0.01). The iodine salt coverage rate and the consumption rate of qualified iodized salt after adjusting the iodine content in iodine salt [93.92% (1 158/1 233), 93.84% (1 157/1 233)]were higher than those before adjusting the iodine content in iodine salt [91.85% (1 138/1 239), 91.37% (1 132/1 239), χ2= 4.01, 5.51, all P < 0.05]. The iodine salt coverage rate and the consumption rate of qualified iodized salt in urban and suburb areas after adjusting the iodine content in iodine salt [99.42% (510/513), 100.00% (203/203), 97.86% (502/513), 100.00% (203/203)] were higher than those before adjusting the iodine content in iodine salt [86.71% (450/519), 98.00% (196/200), 77.26% (401/519), 85.00% (170/200)], but the iodine salt coverage rate and the consumption rate of qualified iodized salt in rural area before adjusting the iodine content in iodine salt [94.62% (492/520), 86.92% (452/520)] were higher than those after adjusting the iodine content in iodine salt [85.69% (443/517), 76.98% (398/517), χ2= 64.22, 2.32, 100.02, 32.90, 23.31, 17.33, all P < 0.05]. One thousand two hundred and thirty-four and one thousand two hundred and thirty-one household urine samples were collected before and after adjusting the iodine content in iodine salt. The median of urinary iodine (MUI, 114.80 μg/L) of pregnant women after adjusting the iodine content in iodine salt was lower than that before adjusting the iodine content in iodine salt (168.60 μg/L, χ2= 36.92, P < 0.01). The MUIs of pregnant women in urban, suburban, and rural areas (171.30, 170.20 and 162.40 μg/L) before adjusting the iodine content in iodine salt were higher than those after adjusting the iodine content in iodine salt (101.00, 149.48 and 119.90 μg/L, χ2=-7.78, -2.63, -6.28, all P < 0.01). The differences of urinary iodine between groups were statistically significant in urban, suburban and rural areas after adjusting the iodine content in iodine salt (χ2= 32.86, P < 0.01), the MUI of pregnant women in urban areas was lower than those in the suburban and rural areas (χ2= 6.70, 8.13, all P < 0.05). Conclusions After adjusting the iodine content of salt in Hangzhou, the iodine-nutrition level of pregnant women is decreased. But the consumption rates of qualified iodized salt and the MUIs in urban, suburb, rural areas are different, so the coverage of iodized salt at household level needs to be enhanced and the health education should be highlighted. Key words: Iodine; Nutrition assessment; Pregnancy; Salt iodization