Nausea and vomiting (NV), fatigue, stress and social support during pregnancy have been well documented using cross-sectional research designs. However, few studies have addressed the patterns and relationships for these variables using a longitudinal research design. The purpose of this study was to examine the patterns of and relationships among NV, fatigue, perceived stress, and social support in pregnant women throughout the three trimesters. A prospective and longitudinal study was conducted from 2003 to 2005. Data were collected on four different measures: the Index of Nausea, Vomiting, and Retching (INVR), the Visual Analog Fatigue Scale (VAFS), the Perceived Stress Scale (PSS), and the Brief Social Support Questionnaire (BSSQ). A total of 91 pregnant women were recruited from prenatal clinics in southern Taiwan. One-way ANOVA indicated that INVR scores and fatigue were significantly different among the three trimesters, but that perceived stress and social support were not. Post hoc analyses, using least significant difference testing, indicated that the first trimester was associated with significantly higher levels of NV than were the second and third trimesters. The first and third trimesters had significantly higher fatigue levels than did the second trimester. Mixed models indicated that the differences among INVR scores among the three trimesters were independent of gravidity, planned pregnancy and age. The difference in fatigue between the first and second trimesters was independent of gravidity, planned pregnancy and age, but fatigue was positively associated with NV. Perceived stress was positively correlated with NV. However, when further examining the relationships among the key variables by adding fatigue, perceived stress was found to positively correlate with fatigue and not NV, and negatively correlated with social support. The findings of this study provide a more comprehensive understanding and evidence-based data of the patterns of and relationships among the above four key variables for pregnant women throughout the three trimesters. This will help health care professionals to provide more effective and appropriate care strategies based on the different stages of pregnancy.