Background: Congenital Zika virus (ZIKV) syndrome is a newly identified condition resulting from infection during pregnancy. We analyzed outcome data from a mother-infant cohort in Rio de Janeiro in order to assess whether clinical severity of maternal ZIKV infection was associated with maternal virus load, prior dengue antibodies or abnormal pregnancy/infant outcomes. Methods: A clinical severity assessment tool was developed based on duration of fever, severity of rash, multisystem involvement and duration of symptoms during ZIKV infection. ZIKV-RNA load was quantified by PCR cycles in blood/ urine. Dengue IgG antibodies were measured at baseline. Adverse outcomes were defined as fetal loss or a live infant with grossly abnormal clinical or brain imaging findings. Regression models were used to study potential associations. Results: 131 ZIKV-PCR positive pregnant women were scored for clinical disease severity, 6 (4.6%) had mild disease, 98 (74.8%) had moderate disease and 27 (20.6%) severe manifestations of ZIKV infection. There were 58 (46.4%) abnormal outcomes with 9 fetal losses (7.2%) in 125 pregnancies. No associations were found between: disease severity and abnormal outcomes (p=0.961; OR:1.00; 95%CI: 0.796- 1.270); disease severity and viral load (p = 0.994); viral load and adverse outcomes (p=0.667; OR:1.02; 95%CI: 0.922- 1.135); or existence of prior dengue antibodies (88% subjects) with severity score, ZIKV-RNA load or adverse outcomes (p = 0.667; OR 0.78; 95%CI : 0.255 - 2.397). Conclusions: Congenital ZIKV syndrome does not appear to be associated with maternal disease severity, ZIKV-RNA load at time of infection or existence of prior dengue antibodies.