The purpose of this study was to compare the folate and vitamin B (12) levels in pregnant and nonpregnant women to evaluate the risk for hyperhomocysteinemia and for folate and vitamin B (12) deficiencies during pregnancy. Healthy pregnant women (n = 92; 24 to 28 gestational weeks; 18 to 39 years old) and nonpregnant women (n = 176; 18 to 39 years old) were sampled for serum levels of folate, vitamin B (12), and homocysteine. Pregnant women were less likely to have folate deficiency (8.0% versus 12.0%) but much more likely to have vitamin B (12) deficiency (46.1% versus 0.6%) than nonpregnant women. Those with lower dietary vitamin intakes were more likely to have vitamin B (12) deficiency. Serum folate and vitamin B (12) were negatively correlated with homocysteine among pregnant women. Pregnant women with folate deficiency were more likely to have hyperhomocysteinemia than those without folate deficiency. The vitamin B (12) level associated with hyperhomocysteinemia was lower in pregnant subjects than in nonpregnant subjects in this study, indicating that pregnant women require vitamin B (12) supplementation.