• Newborn birth weight. [ Time Frame: Within 24 hours of delivery. ] [ Designated as safety issue: No ]
  

• Newborn congenital anomalies. [ Time Frame: Delivery, within 2-6 days of delivery, and 28 days of life. ] [ Designated as safety issue: Yes ]
  
• Pre-eclampsia. [ Time Frame: 22 weeks and 32 weeks. ] [ Designated as safety issue: Yes ]
  
• Parasitological response to treatment. [ Time Frame: Measured at 22 weeks gestation. ] [ Designated as safety issue: Yes ]
  
• Newborn hemoglobin and iron status. [ Time Frame: At 2-6 days of life. ] [ Designated as safety issue: Yes ]
  
• Praziquantel (PZQ) toxicology. [ Time Frame: Just before the dose at 12-16 weeks gestation (baseline) and 24 hours after the second part of the split dose and before discharge from the hospital. ] [ Designated as safety issue: No ]
  
• Pharmacokinetics. [ Time Frame: 4.5 and 8 hours after the first praziquantel dose (subjects assigned to an even study number) or 6 and 10 hours after the first praziquantel dose (subjects assigned to an odd study number). ] [ Designated as safety issue: No ]
  
• Maternal weight gain. [ Time Frame: From 12-16 weeks to 32 weeks. ] [ Designated as safety issue: Yes ]
  
• Extra-placental mechanisms mediating improved outcomes in the praziquantel group. These factors will relate to both birthweight and iron status of the newborn. [ Time Frame: 32 weeks. ] [ Designated as safety issue: Yes ]
  
• Maternal hemoglobin and iron status, assessment of anemia of inflammation. [ Time Frame: Hemoglobin and iron status will be measured at 14 (+/- 2) weeks and 32 weeks. ] [ Designated as safety issue: No ]
  

This double-blind, placebo-controlled study will investigate praziquantel (PZQ) for the treatment of Schistosomiasis japonicum in pregnant women living in endemic villages of Leyte, The Philippines. The study will enroll 500 pregnant women, ages 18 and over, infected with S. japonicum. The primary study objective is to quantify the efficacy of PZQ treatment for S. japonicum at 12-16 weeks gestation on newborn birth weight among live births. This will be assessed by measuring birth weight within 96 hours of delivery to 10 grams. The first secondary objective is to assess treatment efficacy with respect to maternal and newborn nutritional status and maternal parasitologic response to treatment. This will be assessed by evaluating: maternal iron status (ferritin and serum transferrin receptor) and hemoglobin at 32 weeks gestation; change in maternal nutritional status from first trimester to 32 week visit; newborn iron stores as assessed by cord blood ferritin and hemoglobin; and parasitologic response to treatment reported as percent reduction in egg counts from the mean S. japonicum eggs per gram of stool at screening to the mean S. japonicum eggs per gram of stool at 22 weeks gestation. "Successful" treatment will be defined as a 90% or greater reduction in egg counts from pre-treatment to 22 weeks gestation. The second secondary objective is to collect preliminary safety and toxicity data on use of PZQ among pregnant women and their newborns. This will be assessed by evaluating: incidence of maternal convulsion after PZQ dosing; toxicity to maternal bone marrow, kidney, and liver as measured by laboratory parameters collected just before, and 24-48 hours after dose; immediate toxicity to the fetus as assessed by abortion (fetal demise before 20 weeks gestation); and long-term toxicity to the fetus as assessed by rates of pre-maturity measured by modified Dubowitz exam at delivery, low-birth weight, stillbirth as defined by fetal demise after 20 weeks gestation, congenital anomalies as determined by physical exam performed by a pediatrician at 28 days of life; and pharmacokinetics of PZQ during pregnancy as assessed by 2 blood draws (4.5 and 8 hours after the first dose or 6 and 10 hours after the first dose). The third secondary objective is to identify extra-placental mechanisms mediating the hypothesized beneficial effect of PZQ on birth outcomes. The hypothesized mechanisms include: improved maternal iron bio-availability for transfer to the developing fetus and improved maternal nutritional status as assessed by anthropometric measures of body size. The fourth secondary objective is to identify extra-placental mechanisms mediating the hypothesized beneficial effect of PZQ on birth outcomes. The hypothesized mechanisms include: decreased concentrations of tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, and interleukin (IL)-6 and increased concentrations of IL-10 compared in placental blood from S. japonicum infected, PZQ treated mothers compared to untreated mothers; decreased secretion of TNF-alpha, IFN-gamma, and IL-6 and more IL-10 secretion from placental explants from S. japonicum infected, PZQ treated women when stimulated with soluble parasite egg antigen compared to placental explants from S. japonicum infected, PZQ untreated mothers; and lower level of apoptosis in cultured trophoblasts exposed to peripheral serum as measured by cytokeratin 18 neo-epitope staining among S. japonicum infected, PZQ treated mothers versus untreated mothers. Participants will be involved in study related procedures for 9 months (8 months pre-natally and 1 month post-natally) for mother and infant.