Plasmodium falciparum rosette formation is uncommon in isolates from pregnant women

We examined the formation of Plasmodium falciparum erythrocyte rosettes usi ng parasite isolates from placental or peripheral blood of pregnant Malawia n women and from peripheral blood of children. Five of 23 placental isolate s, 23 of 38 maternal peripheral isolates, and 136 of 139 child peripheral i solates formed rosettes. Placental isolates formed fewer rosettes than mate rnal isolates (range, 0 to 7.5% versus 0 to 33.5%; P = 0.002), and both for med fewer rosettes than isolates cultured from children (range, 0 to 56%; P < 0.0001). Rosette formation is common in infections of children but uncom mon in pregnancy and rarely detected in placental isolates.