Abstract: Feeding intolerance (FI) is a common clinical problem in preterm infants often caused by some neonatal disorders and drugs, including antenatal exposure to magnesium sulfate (MgSO4 ). To evaluate the association between hypermagnesemia at birth and FI in preterm infants during the first 72?h of life. This was a cohort study conducted with preterm infants aged <34 weeks' gestation. Infants presenting at least two of the following signs were considered as having FI: vomiting, abdominal distension, the need for continuous intermittent feeding, and delayed meconium passage. Hypermagnesemia was characterized by umbilical serum Mg levels?>?2.5?mEq/L. A total 251 infants were evaluated. The median birth weight and gestational age were 1390?g (IQR, 1020-1070) and 31 weeks (IQR, 28-32). The FI rate was 17.5%. The exposure rate to MgSO4 was similar in the tolerant and intolerant groups (53.1%?×?63.6%; P?=?0.204), but hypermagnesemia was more frequent in the FI group (40.9%?×?24.2%; P?=?0.024). The univariate analysis showed that infants with hypermagnesemia were twofold more likely to present FI (odds ratio [OR], 2.16; 95% CI, 1.09-4.26). In the multiple logistic regression analysis, we found that hypermagnesemia was independently associated with FI (OR, 2.51; 95% CI, 1.06-5.91), as well as maternal diabetes mellitus (OR, 2.56; 95% CI, 1.07-6.14), Score for Neonatal Acute Physiology-Perinatal Extension II (OR, 1.051; 95% CI, 1.025-1.078), and brain hemorrhage (OR, 3.61; 95% CI, 1.31-9.91). In addition to other factors, hypermagnesemia at birth was independently associated with early FI in preterm infants Ver menos