The purpose of this study was to compare physiological and psychological reactions among Taiwanese women with different degrees of severity of nausea and vomiting (NV) during pregnancy. Based on their scores on the Index of Nausea, Vomiting, and Retching (INVR), 59 pregnant women ≥ 18 years of age, with single gestations and without diagnosed pregnancy complications or hospitalizations were divided into two groups: mild or less (scores 0-8, n = 33) and moderate or severe (scores 9-32, n = 26). A single blood sample was obtained early in pregnancy during a prenatal visit to examine the biochemical data related to NV and stress. The INVR and Perceived Stress Scale were also administered at this time. Human chorionic gonadotropin (hCG) and leptin levels were significantly different between the two groups, whereas IFN-α, IL-2, TNF-α, adiponectin, perceived stress, and cortisol showed no significant differences. The cutoff point between high and low levels of NV severity was consistent between INVR scores (psychological reactions) and hCG level (physiological reactions). Logistic regression analysis indicated that leptin levels accounted for 24.4% of the variance for NV in early pregnancy. A further multiple linear regression analysis showed that NV, first trimester pregnancy body mass index (BMI), and age explained 72.4% of the variance in leptin levels. The findings of this study add new information to the understanding of the biomarkers and perceived emotional stress in early-stage pregnant women with high and low severities of NV.