Post-bariatric weight loss can cause iatrogenic malnutrition and micronutrient depletion. In this study, we evaluated the impact of gastric bypass surgery (GB) and multivitamin supplement use on maternal micronutrient status before and across pregnancy. A retrospective medical chart review of 197 singleton pregnancies after GB with a due date between 2009 and 2019 was performed at a bariatric expertise center in the Netherlands. Hemoglobin, calcium, iron status, folate, vitamin D, vitamin B12 and ferritin levels were determined before and after GB during standard follow-up and at all gestational trimesters and analyzed using linear mixed models. Patients were prescribed standard multivitamin supplements or multivitamins specifically developed for post-bariatric patients (FitForMe WLS Forte (FFM)). Overall, hemoglobin and calcium levels decreased after surgery and during pregnancy, whereas folate, vitamin D, and vitamin B12 levels increased, and iron levels remained stable. FFM use was associated with higher hemoglobin, folate, vitamin D, and ferritin levels. In conclusion, through adequate supplementation and follow-up, GB does not have to result in impaired micronutrient status. Supplements developed specifically for post-bariatric patients generally result in higher micronutrient values than regular multivitamins before and during pregnancy. These data emphasize the urgent need for nutritional counseling including dietary and multivitamin supplement advise for post-bariatric women contemplating and during pregnancy.