- Objective The objective of the study was to investigate pregnancy outcome of patients with gestational diabetes mellitus following bariatric surgery. Study design All births to patients with gestational diabetes mellitus delivered between the years 1988 and 2002 were included in the study. A comparison between patients with and without a history of bariatric surgery was performed. Stratified analyses, using the Mantel-Haenszel technique and a multiple logistic regression model were performed to control for confounders. Results During the study period, there were 8014 deliveries of women with gestational diabetes mellitus. Twenty-eight were in patients following bariatric surgery. Most patients underwent restrictive (n = 26) and not malabsorptive procedures (n = 2), mainly gastric banding (n = 16). Mean levels of hemoglobin A1c and fasting glucose were comparable between the groups. No significant differences in obstetric characteristics or pregnancy outcomes were noted between the patients following bariatric surgery as compared with the comparison group, except for higher rates of fertility treatments (21.4% versus 5.5%; P < .001). While controlling for nulliparity and maternal age, using a multivariable analysis, a significant association was noted between bariatric surgery and fertility treatments (odds ratios 4.7; 95% confidence interval 1.9 to 11.7; P = .001). Perinatal outcome was comparable between the groups, and no significant differences were noted with regard to complications such as perinatal mortality, congenital malformations, and low Apgar scores at 1 and 5 minutes. Conclusion Previous bariatric surgery in patients with gestational diabetes mellitus is not associated with adverse perinatal outcome.