Healthy women at 12 weeks’ gestation and over from four different areas in Zhejiang province were enrolled to participate this program from May 2007 to May 2010. Women consented to provide urine samples and salt samples during pregnancy (12, 16, 24 weeks’ gestation and before delivery), and give permission to access their newborn’s TSH value. Urinary iodine concentration (UIC) was determined by ammonium persulfate digestion microplate method, and TSH was determined by a time resolved fluoro-immunoassay (TRFIA). The diagnostic standard for congenital hypothyroidism was: TSH ≥ 20 mU/L and declined FT4 levels. Compare the correlation to effects with different level of iodine content in salt, maternal UIC and neonatal TSH. Investigate the optimal level of iodine content in salt in different areas in ZheJiang province.