hCG levels in early pregnancy are hypothesized to reflect trophoblast function and placental health. The goal of this study was to examine the association between serial hCG levels and maternal and perinatal outcomes. Retrospective cohort study. Patients with symptomatic unassisted pregnancies were followed with early first trimester serial hCGs. Only singleton live births were included. The slope for daily rate of increase in log transformed hCG levels (hCG rise) was estimated and analyzed as a continuous variable and by quartile (Q). Primary outcomes were birth weight and gestational age at delivery. Secondary outcomes were preterm birth, low birth weight (<2,500g), and hypertensive disorders. The relationship of hCG rise with each outcome was assessed with t-tests, chi-square tests, and linear and logistic regression. 159 singleton live births were analyzed. The median two-day increase in hCG was 105% (lower Q 70%; upper Q 142%). Linear regression models demonstrated no significant association between hCG rise and birth weight or gestational age. However, quartile of hCG rise was significantly associated with low birth weight (P=0.002). Compared to the first Q (slowest), subjects with a more rapid hCG rise (second-fourth Qs) had increased odds of low birth weight (OR 18.78, 6.54, and 5.14, respectively). A composite outcome, including small for gestational age, low birth weight, preterm birth, and preeclampsia was also more prevalent in higher Qs of hCG rise (P=0.006, OR 5.83, 3.75, and 1.54, respectively). A similar trend was observed for a composite adverse infant outcome (P=0.023, OR 4.62, 7.93, and 3.26, respectively). The rise in hCG may reflect trophoblast cell differentiation and function. A fast rise may indicate suboptimal placental function. These findings could lead to an early method to identify women at risk for later pregnancy complications.