The SuNDiAL study will measure levels of two naturally occurring amino acids: Arginine and Asymmetric Dimethylarginine (ADMA) in neonates undergoing abdominal surgery in the first 5 days of life due to congenital abdominal malformations as the participants recover from surgery. The investigators hypothesise that the relationship between Arginine and ADMA may be useful in predicting recovery and complications in babies who have had abdominal surgery due to previous research published in adult patients undergoing abdominal surgery. If this relationship is found to be useful there may be options for developing treatments (such as arginine supplementation) in the future to improve recovery and reduce complications in neonates undergoing abdominal surgery. Neonates born after 35 weeks gestation who have a congenital abdominal malformation who require abdominal surgery in the first 5 days will be eligible to participate in the SuNDiAL study. Arginine and ADMA will be measured from blood samples that are left over from the participant's blood tests that are taken as part of their routine clinical care. The investigators will measure Arginine and ADMA preoperatively and at least 10 points in the 30 days following their surgery, or until the participant fully recovers from surgery (which ever comes first). There is no intervention in the SuNDiAL study, and there will be no extra blood or blood samples taken. Serums samples that are left over from the babies routine clinical blood tests will be stored securely in the hospitals laboratory until analysis for Arginine and ADMA. The levels of Arginine and ADMA will be compared to the time it takes the participants to recover from surgery and any complications that may arise following surgery. During the study the study team will use the participants electronic medical record to establish when the participant became fully established on oral feeding and monitor for any complications that occurred during their recovery.