Book excerpt: Despite low socioeconomic status and lack of resources, Latinas are found to have better-than-expected birth outcomes, which deteriorate with higher US acculturation. In addition, as the incidence of obesity rises amongst Latinas, it is necessary to study this acculturation paradox in the context of obesity. The purpose of this study was to examine the association between US acculturation and poor birth outcomes, particularly examining preterm birth and/or low birth weight (PTLBW), in a sample of Mexican origin women. Furthermore, the differential effect of obesity on the association between acculturation and birth outcomes was examined. This was a longitudinal observational study using data from the Study for Hispanic Acculturation, Reproduction, and the Environment (SHARE). Participants were 1,062 pregnant women recruited from six Obstetrics and Gynecology Clinics in San Joaquin County, California between 1999 and 2001. The majority of women were of Mexican descent at varying lengths of US residency. Logistic regression analysis was used to examine the associations among acculturation, obesity and poor birth outcomes. Results demonstrated a significant association between US acculturation and PTLBW such that moderately acculturated women had over three times the odds of experiencing PTLBW, while low and highly acculturated women did not show an increased risk. In moderately acculturated women who were also obese, their chance of PTLBW decreased, indicating that obesity acted as a buffer for PTLBW. This effect was not demonstrated in low or highly acculturated women. In conclusion, this study re-examines the Latina Acculturation Paradox in the context of obesity. It is unique in that it demonstrates deviation from the paradox, as the most highly acculturated women did not experience the worst birth outcomes. Additionally, this is among the first study to demonstrate a protective effect of obesity in terms of perinatal health.