Fifty-six human immunodeficiency virus seropositive-women and 76 human immunodeficiency virus seronegative-women had known CD4 cell values and were followed up throughout pregnancy. The women with seronegative results and the 40 with seropositive results and CD4 (helper cell) counts consistently greater than 300 cells/mm3 had no serious infections during pregnancy. Among the 16 with seropositive results and counts that fell below 300 cells/mm3, three developed opportunistic infections, one had pneumonia, and one had a post-cesarean-section abscess. Human immunodeficiency virus seropositive-women with low CD4 counts are at markedly increased risk of serious infections during pregnancy. The consequences of this for fetal health, pregnancy management, maternal well-being, and human immunodeficiency virus testing policies are discussed.