Since 1993, the People's Republic of China has recommended that newly married women, and those who plan pregnancy, take 400μg of folic acid daily through the first trimester of pregnancy. Although WHO recommends that pregnant women take iron and folic acid supplements, there is currently no national recommendation that pregnant women in China take iron or other vitamin or mineral supplements (other than folic acid). UNICEF is now testing a prenatal vitamin and mineral supplement in programs to prevent low birth weight. Our study will provide additional information about the health impact of the UNICEF prenatal supplement versus an iron and folic acid supplement versus folic acid alone.