hydroxychloroquine: anti-inflammatory drug (trade name Plaquenil) used in the treatment of rheumatoid arthritis and malaria and lupus erythematosus
causal agent: any entity that produces an effect or is responsible for events or results
placenta previa: pregnancy in which the placenta is implanted in the lower part of the uterus (instead of the upper part); can cause bleeding late in pregnancy; delivery by cesarean section may be necessary