In malaria-endemic regions, strategies to control malaria during pregnancy rely on case management of malaria illness and anemia, and preventive measures such as insecticide-treated nets and intermittent preventive therapy (IPT). To determine the effect of increasing resistance to sulfadoxine-pyrimethamine on the efficacy of IPT during pregnancy in Africa. The 6 databases of MEDLINE, EMBASE, SCOPUS, LILACS, Cochrane CENTRAL, and the trial register and bibliographic database of the Malaria in Pregnancy Library were searched for relevant studies regardless of language, published between 1966 and December 2006. The reference lists of all trials identified were searched and researchers were contacted about relevant data. Nine trials of IPT with sulfadoxine-pyrimethamine during pregnancy in Africa were identified and matched by year and location with treatment studies of sulfadoxine-pyrimethamine among symptomatic children. Data on the efficacy of IPT with sulfadoxine-pyrimethamine on placental and peripheral malaria, birth weight, and hemoglobin level/anemia were independently abstracted by 2 investigators. Sulfadoxine-pyrimethamine resistance was defined as the proportion of total treatment failures in symptomatic children by day 14. Four trials compared 2-dose IPT with sulfadoxine-pyrimethamine to case management or placebo in women during their first or second pregnancy. The IPT reduced placental malaria (relative risk [RR], 0.48; 95% CI, 0.35-0.68), low birth weight (RR, 0.71; 95% CI, 0.55-0.92), and anemia (RR, 0.90; 95% CI, 0.81-0.99). The effect did not vary by sulfadoxine-pyrimethamine resistance levels (range, 19%-26%). Efficacy of IPT with sulfadoxine-pyrimethamine was lower among women using insecticide-treated nets. Three trials compared 2-dose with monthly IPT with sulfadoxine-pyrimethamine during pregnancy. Among HIV-positive women in their first or second pregnancy, monthly IPT resulted in less placental malaria (RR, 0.34; 95% CI, 0.18-0.64) and higher birth weight (mean difference, 112 g; 95% CI, 19-205 g) over the range of sulfadoxine-pyrimethamine resistance tested (8%-39%). Among HIV-negative women, there was no conclusive additional effect of monthly dosing (2 trials; 24% and 39% resistance). In areas in which 1 of 4 treatments with sulfadoxine-pyrimethamine fail in children by day 14, the 2-dose IPT with sulfadoxine-pyrimethamine regimen continues to provide substantial benefit to HIV-negative semi-immune pregnant women. However, more frequent dosing is required in HIV-positive women not using cotrimoxazole prophylaxis for opportunistic infections.