Objectives To describe the dietary patterns in pregnant woman and determine the association between diet factors, pre-pregnancy Body Mass Index (BMI) and socio-demographic characteristics with gestational weight gain (GWG). Methods This is a secondary analysis of a longitudinal cohort study of pregnant women exploring the risk factors for preterm birth, the Puerto Rico Testsite for Exploring Contamination Threats program. Recruitment was conducted during 2011–2014. Data was collected from multiple sources. GWG was calculated using maternal weight recorded in the medical records at the first and last prenatal visits and classified according to the Institute of Medicine guidelines. Sociodemographic characteristics were obtained at baseline using an interviewed-based questionnaire. Participants completed a self-administered food frequency questionnaire at 20–28 weeks to assess dietary patterns. Analysis of associations between variables was conducted using Chi Square tests. Results A total of 160 women with term pregnancies were included in this analysis. Mean pre-pregnancy BMI was 25.4 ± 5.48 kg/m2, with 44.4 % classified as overweight/obese. Excessive GWG was observed in 24.4 % of the participants. Socio-demographic characteristics were not associated with GWG. Being overweight/obese at the start of pregnancy was significantly associated with excessive GWG (p < 0.05). In addition, women consuming one or more fruit drinks per day were more likely to have an excessive GWG while those consuming less than one fruit drink per day were more likely to have an adequate GWG (p < 0.05). Conclusions for Practice Being obese before pregnancy and frequently consuming fruit drinks were important determinants of excessive GWG in this group.