Hi Thanks for posting your query on HCM. I appreciate your concern for your wife. Because of its efficacy and safety Injection Insulin is the gold standard treatment for Gestational diabetes mellitus. Diarrhea, flatulence, abdominal cramps, nausea and vomiting are important side effects of Glycomet. Since she is having gestational diabetes if diarrhea is not controlled with the adjustment of the dose of Glycomet (as her treating doctor might suggest) she may need to take Inj Insulin for the control of high blood glucose level. Besides, other causes of diarrhea (like gastroenteritis, amebiasis, etc) should be investigated (stool analysis) for and treated accordingly. Hope this answers your query. Rate this answer, if you are convinced.