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Each year, 24% of births in resource poor countries are small-for-gestational age (SGA). Most SGA infants suffer from intrauterine growth restriction (IUGR); a pathologic process characterized by insufficient transfer of nutrients and oxygen to the fetus and impaired fetal growth. In resource poor countries, IUGR is frequently due to malaria or maternal under-nutrition. This dissertation addresses clinically important questions concerning the pathogenesis of malaria infection in utero and the identification of IUGR in resource poor settings. The data source is a prospective, longitudinal ultrasound study of 182 pregnant women conducted in Kinshasa, Democratic Republic of Congo between May 2005 and May 2006. Women participated in monthly follow-up visits during which malaria, maternal anthropometrics, and ultrasound estimated fetal weight (EFW) were measured. We estimated the effect of malaria on the risk of IUGR, and assessed whether maternal under-nutrition modified this relationship. Data from 178 women and 758 ultrasounds were included. IUGR was defined as EFW below the 10th percentile of a standardized fetal weight nomogram. Log-binomial models using generalized estimating equations were fitted separately for malaria and maternal anthropometric exposures and including a product interaction term between them. A single incident malaria infection was not significantly associated with IUGR (Risk ratio (RR)=1.2, 95% confidence interval (CI): 0.7, 2.2); women with [greater than or equal to] 3 episodes were at increased risk (RR=2.3, 95% CI: 0.8, 6.3). The effect of malaria was significantly stronger among under-nourished women. Prompt treatment of antenatal malaria infections may prevent IUGR, especially in under-nourished women. We developed a fetal size nomogram for Congo using data from 144 women with certain gestational dates and 755 ultrasound scans. A linear mixed effect model was fitted for EFW as a function of gestational age that incorporated random effects for the intercept and slope. Reference intervals were derived from this model and compared with intervals derived from industrialized countries. The 50th centile EFW for Congo fetuses was consistently lower than fetuses born in industrialized populations. Comparison of the outer centiles showed inconsistent patterns, owing primarily to differing statistical techniques. This fetal size nomogram should improve diagnosis of IUGR in resource poor settings with endemic malaria.